Methods of inhibiting corrosion with a pyrazine corrosion inhibitor

ABSTRACT

A method of inhibiting corrosion of metal during acid stimulation of an oil and gas well, whereby the oil and gas well is treated with an acidic treatment fluid that includes 10 to 28 wt. % of an acid, based on a total weight of the acidic treatment fluid, and 0.01 to 5% of a pyrazine corrosion inhibitor by weight per total volume of the acidic treatment fluid, wherein the pyrazine corrosion inhibitor is 2,3-pyrazine dicarboxylic acid, pyrazine-2-carboxamide, 2-methoxy-3-(1-methylpropyl) pyrazine, or combinations thereof.

STATEMENT OF ACKNOWLEDGEMENT

The authors would like to acknowledge the support received from KingAbdulaziz City for Science and Technology (KACST) for funding this workunder the National Science Technology Plan (NSTIP) grant No.14-ADV2448-04. Also, the support provided by the Deanship of ScientificResearch (DSR) and the Center of Research Excellence in Corrosion(CORE-C), at King Fahd University of Petroleum & Minerals (KFUPM) isgratefully acknowledged.

STATEMENT REGARDING PRIOR DISCLOSURE BY THE INVENTORS

Aspects of this technology are described in an article “Pyrazinederivatives as green oil field corrosion inhibitors for steel” publishedin Journal of Molecular Liquids, 2019, 277, 749-761, available online onDec. 22, 2018, which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to methods of inhibiting corrosion ofmetal during acid stimulation operations with acidic treatment fluidscontaining a pyrazine corrosion inhibitor.

Discussion of the Background

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentinvention.

Corrosion is a persistent issue in the oil and gas industry. This isbecause corrosion issues contribute to a significant portion of theannual budget of this industry. See M. Finšgar, J. Jackson, Applicationof corrosion inhibitors for steels in acidic media for the oil and gasindustry: A review, Corros. Sci. 86 (2014) 17-41—incorporated herein byreference in its entirety. In this regard, employing suitable corrosioncontrol measures can aid in preventing disasters such as spillages, lossof lives and other negative social impacts. See M. M. Osman, M. N.Shalaby, Some ethoxylated fatty acids as corrosion inhibitors for lowcarbon steel in formation water, Mater. Chem. Phys. 77 (2003) 261-269;P. C. Okafor, X. Liu, Y. G. Zheng, Corrosion inhibition of mild steel byethylamino imidazoline derivative in CO2-saturated solution, Corros.Sci. 51 (2009) 761-768; and V. Garcia-Arriaga, J. Alvarez-Ramirez, M.Amaya, E. Sosa, H2S and 02 influence on the corrosion of carbon steelimmersed in a solution containing 3M diethanolamine, Corros. Sci. 52(2010) 2268-2279—each incorporated herein by reference in theirentirety. Corrosion takes place at all production stages in oil and gasindustries, that is, from downhole to surface equipment, processing andwell treatments. See Z. Panossian, N. L. de Almeida, R. M. F. de Sousa,G. de S. Pimenta, L. B. S. Marques, Corrosion of carbon steel pipes andtanks by concentrated sulfuric acid: A review, Corros. Sci. 58 (2012)1-11—incorporated herein by reference in its entirety. Well treatmentprocedures involving the use of either weak or strong acids torejuvenate old wells and remove scales is termed acidizing. See E.Ituen, O. Akaranta, A. James, Electrochemical and anticorrosionproperties of 5-hydroxytryptophan on mild steel in a simulatedwell-acidizing fluid, Integr. Med. Res. (2017) 1-13; Y. K. Choudhary, A.Sabhapondit, A. Kumar, Application of Chicory as Corrosion Inhibitor forAcidic Environments, Society of Petroleum Engineers, Paper No.SPE-155725-PA (2013) 268-276; and L. O. Olasunkanmi, M. F. Sebona, E. E.Ebenso, Influence of 6-phenyl-3(2H)-pyridazinone and3-chloro-6-phenylpyrazine on mild steel corrosion in 0.5 M HCl medium:Experimental and theoretical studies, J. Mol. Struct. 1149 (2017)549-559—each incorporated herein by reference in their entirety. Duringthis treatment, acid is added into the well to enlarge existing flowpathways, open new ones, and also to remove scales. See Y. G. Avdeev, Y.I. Kuznetsov, A. K. Buryak, Inhibition of steel corrosion by unsaturatedaldehydes in solutions of mineral acids, Corros. Sci. 69 (2013) 50-60;E. B. Ituen, O. Akaranta, S. A. Umoren, N-acetyl cysteine basedcorrosion inhibitor formulations for steel protection in 15% HClsolution, J. Mol. Liq. (2017)—each incorporated herein by reference intheir entirety. By so doing pipes and other metallic structures arehighly exposed to these corrosive acids leading to corrosion damage. SeeN. A. A. Ghany, M. F. Shehata, R. M. Saleh, A. A. El Hosary, Novelcorrosion inhibitors for acidizing oil wells, Mater. & Corros. (2017)355-360; U. Eduok, O. Faye, J. Szpunar, Corrosion inhibition of X70sheets by a film-forming imidazole derivative at acidic pH, RSC Adv. 6(2016) 108777-108790—each incorporated herein by reference in theirentirety. The choice of acid for these treatments depends on the stateof the well bore. Hydrochloric acid, sulfuric acid, acetic acid andhydrofluoric acid are some of the commonly used acids in thesetreatments. Hydrochloric acid is highly preferred to other acids sincesalts formed during the process are very soluble in water.

The concentration of the acids utilized in these stimulation treatmentsusually ranges between 15-28% which creates a corrosive environment andthus severe corrosion damage to carbon steel. Carbon steel is the mostwidely used steel due to its relatively cheap cost and abundance. Tomitigate corrosion and related damage, chemical compounds, eitherorganic or inorganic are added to these treatment acids. Numerouscompounds such as quinolines, imidazolines, thioureas, pyridines andtheir various derivatives, alkenylphenones, amines, amides, acetylenicalcohols, and quaternary salts have been employed as corrosioninhibitors of carbon steel during stimulation treatments. See G.Schmitt, Application of Inhibitors for Acid Media: Report prepared forthe European Federation of Corrosion Working Party on Inhibitors, Br.Corros. J. 19 (1984) 165-176; B. D. B. Tiu, R. C. Advincula, Polymericcorrosion inhibitors for the oil and gas industry: Design principles andmechanism, React. Funct. Polym. 95 (2015) 25-45; and W. Frenier, D.Hill, R. Jasinski, Corrosion Inhibitors for Acid Jobs, Oilf. Rev. 1(1989) 15-21—each incorporated herein by reference in their entirety.Other corrosion inhibitors such as sulfoxides, thioethers, mercaptans,thiazoles, thiocyanates, and sulfonium compounds have also been used tocombat corrosion. Historically, chromates and arsenate compounds aresome of the inorganic compounds utilized in stimulation treatments,while acetylenic alcohols have been extensively utilized because oftheir relatively cheap cost and availability. Currently, propargylalcohol and cinnamaldehyde are standard corrosion inhibitors for acidtreatments. See A. Singha, M. A. Quraishi, Acidizing corrosioninhibitors: A review, J. Mater. Environ. Sci. 6 (2015) 224-235; and E.Barmatov, J. Geddes, T. Hughes, M. Nagl, Research on corrosioninhibitors for acid stimulation, NACE-Int. Corros. Conf. Ser. 6 (2012)4604-4623—each incorporated herein by reference in their entirety.

However, the utilization of some of these compounds such as chromates,arsenates and sulfur containing compounds can be hazardous. Chromateshave been shown to be carcinogenic, while arsenates are one of the maincauses of arsenic poisoning. Also, some of the sulfur containingcompounds are degraded in the acid treatment process, thereby formingH₂S that facilitates penetration of hydrogen into the metal and leadingto embrittlement. Due to these toxicity and degradation issues, a majorfocus has been drawn to green and environmental friendly organiccorrosion inhibitor compounds.

Addition of these organic compounds to the corrosive media might impedethe corrosion damage cause to metal surfaces. See A. Popova, M.Christov, A. Zwetanova, Effect of the molecular structure on theinhibitor properties of azoles on mild steel corrosion in 1Mhydrochloric acid, Corros. Sci. 49 (2007) 2131-2143—incorporated hereinby reference in its entirety. The molecules usually adsorb to thesurface of the metal and form complexes through heterogeneous atoms suchas phosphorus, sulfur, oxygen, nitrogen etc. See A. A. Farag, T. A. Ali,The enhancing of 2-pyrazinecarboxamide inhibition effect on the acidcorrosion of carbon steel in presence of iodide ions, J. Ind. Eng. Chem.21 (2015) 627-634; N. C. Oforka, O. K. Abiola, I. Chemistry, P.Harcourt, A. Chemistry, A study on the inhibition of mild steelcorrosion in hydrochloric acid by pyridoxol hydrochloride Ecl. Quim.,SAo Paulo, 32 (2007) 31-38; and A. A. Al-taq, S. Aramco, S. A. Ali, K.Fahd, Inhibition Performance of a New Series of Mono-/Diamine-BasedCorrosion Inhibitors for HCl Solutions, Society of Petroleum Engineers,SPE 114087-Paper (2009) 627-633—each incorporated herein by reference intheir entirety. The inhibition effectiveness of the organic molecules islargely dependent upon interactions between the metal surface-moleculeinterface. See G. Avci, Corrosion inhibition of indole-3-acetic acid onmild steel in 0.5 M HCl, Colloids Surfaces A Physicochem. Eng. Asp. 317(2008) 730-736—incorporated herein by reference in its entirety.Heterogeneous atoms with triple bonds and aromatic rings can form goodcoordination bonds with the surface of metals. Inhibition efficiency isdirectly proportional to the strength of the coordination bond, withhigher coordination bond strengths generally resulting in higherinhibition efficiencies.

With the increased desire to use environmental friendly molecules,numerous studies have been focused on heterocyclic molecules,particularly those containing nitrogen. See F. Bentiss, M. Traisnel, L.Gengembre, M. Lagrenée, Inhibition of acidic corrosion of mild steel by3,5-diphenyl-4H-1,2,4-triazole, Appl. Surf. Sci. 161 (2000) 194-202; A.S. Fouda, H. E. Gadow, Streptoquin and Septazole: Antibiotic drugs ascorrosion inhibitors for copper in aqueous solution, Global J. Res.Engr: C Chem. Eng. 14 (2014) 20-36; K. M. Ismail, Evaluation of cysteineas environmentally friendly corrosion inhibitor for copper in neutraland acidic chloride solutions, Electrochim. Acta. 52 (2007) 7811-7819;A. K. Singh, M. A. Quraishi, Effect of Cefazolin on the corrosion ofmild steel in HCl solution, Corros. Sci. 52 (2010) 152-160; C. Hao, R.H. Yin, Z. Y. Wan, Q. J. Xu, G. D. Zhou, Electrochemical andphotoelectrochemical study of the self-assembled monolayer phytic acidon cupronickel B30, Corros. Sci. 50 (2008) 3527-3533—each incorporatedherein by reference in their entirety. Nitrogen containing heterocycliccompounds such as quinoline, indole, benzimidazole, pyridine and theirvarious derivatives have been shown to inhibit corrosion by adsorbing tothe surface of the steel. See L. Wang, Evaluation of2-mercaptobenzimidazole as corrosion inhibitor for mild steel inphosphoric acid, Corros. Sci. 43 (2001) 2281-2289; A. Popova, M.Christov, S. Raicheva, E. Sokolova, Adsorption and inhibitive propertiesof benzimidazole derivatives in acid mild steel corrosion, Corros. Sci.46 (2004) 1333-1350; G. Moretti, 5-Amino- and 5-chloro-indole as mildsteel corrosion inhibitors in 1 N sulphuric acid, Electrochim. Acta. 41(1996) 1971-1980; and M. Dlidikcil, B. Yazici, M. Erbil, The effect ofindole on the corrosion behaviour of stainless steel, Mater. Chem. Phys.87 (2004) 138-141—each incorporated herein by reference in theirentirety. Inhibitors mostly adsorb on the surface of steel throughcovalent or electrostatics bond formation. Several factors such asprojected surface area of the molecules interacting with the metal, howthe molecules are adsorbed, metal complex formation, size of themolecules, charge density etc. are responsible for the inhibition actionof organic compounds. See M. Kissi, M. Bouklah, B. Hammouti, M.Benkaddour, Establishment of equivalent circuits from electrochemicalimpedance spectroscopy study of corrosion inhibition of steel bypyrazine in sulphuric acidic solution, Appl. Surf. Sci. 252 (2006)4190-4197—incorporated herein by reference in its entirety.

Pyrazine and its derivatives have been used in a wide variety ofapplications such as organic photovoltaics and organic light emittingdiodes, flavoring in food, fragrances, pharmaceutical and agro-basedchemicals, ligands, and other derivatives of pyrazine such as thosecontaining amides and sulfonamides are of significant interest inanti-tuberculosis and anti-diabetic drugs. See S. K. Saha, A. Hens, A.Roychowdhury, A. K. Lohar, Molecular Dynamics and Density FunctionalTheory Study on Corrosion Inhibitory Action of Three SubstitutedPyrazine Derivatives on Steel Surface, Can. Chem. Trans. 2 (2014)489-503—incorporated herein by reference in its entirety; S. C.Rasmussen, R. L. Schwiderski, M. E. Mulholland, Thieno[3,4-b]pyrazinesand their applications to low band gap organic materials, Chem. Commun.47 (2011) 11394; J. Li, Q. Li, D. Liu, Novel thieno-[3,4-b]-pyrazinescored dendrimers with carbazole dendrons: Design, synthesis, andapplication in solution-processed red organic light-emitting diodes, ACSAppl. Mater. Interfaces. 3 (2011) 2099-2107; T. Akiyama, Y. Enomoto, T.Shibamoto, A New Method of Pyrazine Synthesis for Flavor Use, J. Agric.Food Chem. 26 (1978) 1176-1179; T. B. Adams, S. M. Cohen, J. Doull, V.J. Feron, J. I. Goodman, L. J. Marnett, I. C. Munro, P. S. Portoghese,R. L. Smith, W. J. Waddell, B. M. Wagner, The FEMA GRAS assessmentofbenzyl derivatives used as flavor ingredients, Food Chem. Toxicol. 43(2005) 1207-1240; T. Guilford, C. Nicol, M. Rothschild, B. P. Moore, Thebiological roles pf pyrazines: evidence for a worning odour function.,Biol. J. Linn. Soc. 31 (1987) 113-128; R. Goel, V. Luxami, K. Paul,Recent advances in development of imidazo[1,2-a]pyrazines: synthesis,reactivity and their biological applications, Org. Biomol. Chem. 4(2010) 1166-1169; W. W. K. R. Mederski, D. Kux, M. Knoth, J. Markus,Pyrido[3,4-b] pyrazines: A new application of2-Chloro-3,4-diaminopyridine, Heterocycles, 60 (2003) 925-932; P. J.Steel, C. M. Fitchett, Metallosupramolecular silver(I) assemblies basedon pyrazine and related ligands, Coord. Chem. Rev. 252 (2008) 990-1006;and Y. Higashio, T. Shoji, Erratum: Heterocyclic compounds such aspyrrole, pyridines, pyrrolidine, piperidine, indole, imidazol andpyrazines (Applied Cataltysis A: General PII S0926860X01008158), Appl.Catal. A Gen. 260 (2004) 251-259—each incorporated herein by referencein their entirety. Data regarding cytotoxicity, antifungal andantituberculotic properties ofpyrazine derivatives have been widelyreported in literature. See M. Bouklah, A. Attayibat, S. Kertit, A.Ramdani, B. Hammouti, A pyrazine derivative as corrosion inhibitor forsteel in sulphuric acid solution, Appl. Surf. Sci. 242 (2005) 399-406;D.-L. Du, D. A. Volpe, C. K. Grieshaber, M. J. Murphy Jr., Comparativetoxicity of fostriecin, hepsulfam and pyrazine diazohydroxide to humanand murine hematopoietic progenitor cells in vitro, Invest. New Drugs. 9(1991) 149-157; A. Rey, C. Gouedard, N. Ledirac, M. Cohen, J. Dugay, J.Vial, V. Pichon, L. Bertomeu, D. Picq, D. Bontemps, F. Chopin, P. L.Carrette, Amine degradation in CO2 capture. 2. New degradation productsof MEA. Pyrazine and alkylpyrazines: Analysis, mechanism of formationand toxicity, Int. J. Greenh. Gas Control. 19 (2013) 576-583; E. J.Moran, O. D. Easterday, B. L. Boser, Acute oral toxicity of SelectedFlavour Chemicals, Drug Chem. Toxicol. 3 (2015) 249-258; and J. J.Kaminski, D. G. Perkins, J. D. Frantz, D. M. Solomon, A. J. Elliott, P.J. S. Chiu, J. F. Long, Antiulcer Agents. 3. Structure-Activity-ToxicityRelationships of Substituted Imidazo[1,2-a]pyridines and a RelatedImidazo[1,2-a]pyrazine, J. Med. Chem. 30 (1987) 2047-2051—eachincorporated herein by reference in their entirety. Moreover pyrazinesare cost effective and environmentally friendly since they are widelyused as flavoring agents in food.

Xianghong et al reported on the effectiveness of three pyrazinederivatives, that is, 2-aminopyrazine, 2-amino-5-bromopyrazine and2-methylpyrazine in 1 M H₂SO₄ and concluded that these pyrazinemolecules are generally effective corrosion inhibitors. See XianghongLi, Shudduan Deng, and Hui Fu, Three pyrazine derivatives as corrosioninhibitors for steel in 1.0 M H₂SO₄ solution, Corrosion Science, 2011,53 (10), 3241-3247—incorporated herein by reference in its entirety.2-amino-5-bromopyrazine was found to be most effective followed by2-aminopyrazine and finally 2-methylpyrazine as the least effective.Deng et al studied the inhibition efficiency of 2-amino-5-bromopyrazineand 2-aminopyrazine in 1M HCl and found out that these two pyrazinederivatives are good corrosion inhibitors and they observed that2-amino-5-bromopyrazine was more effective compared to 2-aminopyrazine.See S. Deng, X. Li, H. Fu, Two pyrazine derivatives as inhibitors of thecold rolled steel corrosion in hydrochloric acid solution, Corros. Sci.53 (2011) 822-828—incorporated herein by reference in its entirety.Kissi et al studied inhibition performance ofdiethylpyrazine-2,3-dicarboxylate in 0.5 M H₂SO₄ and found thatefficiency increased with concentration of the inhibitor and the highestefficiency attained was 82% at a concentration of 5×10⁻³M. See M. Kissi,M. Bouklah, B. Hammouti, M. Benkaddour, Establishment of equivalentcircuits from electrochemical impedance spectroscopy study of corrosioninhibition of steel by pyrazine in sulphuric acidic solution, Appl.Surf. Sci. 252 (2006) 4190-4197—incorporated herein by reference in itsentirety. Bouklah et al also studied the performance ofdiethylpyrazine-2,3-dicarboxylate in 0.5 M H₂SO₄ and found thatdiethylpyrazine-2,3-dicarboxylate adsorbs to the metal surface accordingto Langmuir model. See M. Bouklah, A. Attayibat, S. Kertit, A. Ramdani,B. Hammouti, A pyrazine derivative as corrosion inhibitor for steel insulphuric acid solution, Appl. Surf. Sci. 242 (2005)399-406—incorporated herein by reference in its entirety. It was alsoobserved that diethyl pyrazine-2,3-dicarboxylate acts as a cathodicinhibitor with efficiency up to 82%.

In view of the forgoing, there is a need for inexpensive, effective, andnon-toxic corrosion inhibitors that can be used either alone or incorrosion inhibiting formulations in low dosages, for preventingcorrosion of metal in various oil and gas field environments, includinghigh temperature and highly acidic conditions common to acid stimulationoperations.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the present invention to provide novelmethods of inhibiting corrosion of metal during acid stimulation of anoil and gas well using acidic treatment fluids containing highconcentrations of acids and low concentrations of a cheap and non-toxicpyrazine corrosion inhibitor.

Thus, the present invention provides:

A method of inhibiting corrosion of metal during acid stimulation of anoil and gas well, the method involving treating the oil and gas wellwith an acidic treatment fluid comprising 10 to 28 wt. % of an acid,based on a total weight of the acidic treatment fluid, and 0.01 to 5% ofa pyrazine corrosion inhibitor by weight per total volume of the acidictreatment fluid, wherein the pyrazine corrosion inhibitor is at leastone selected from the group consisting of 2,3-pyrazine dicarboxylicacid, pyrazine-2-carboxamide, and 2-methoxy-3-(1-methylpropyl) pyrazine.

In some embodiments, the pyrazine corrosion inhibitor is present in theacidic treatment fluid in a concentration of 0.2 to 1% by weight pertotal volume of the acidic treatment fluid.

In some embodiments, the pyrazine corrosion inhibitor is 2,3-pyrazinedicarboxylic acid, and wherein 2,3-pyrazine dicarboxylic acid is presentin the acidic treatment fluid in a concentration of 0.2 to 1% by weightper total volume of the acidic treatment fluid.

In some embodiments, the pyrazine corrosion inhibitor ispyrazine-2-carboxamide, and wherein pyrazine-2-carboxamide is present inthe acidic treatment fluid in a concentration of 0.8 to 1% by weight pertotal volume of the acidic treatment fluid.

In some embodiments, the pyrazine corrosion inhibitor is2-methoxy-3-(1-methylpropyl) pyrazine, and wherein2-methoxy-3-(1-methylpropyl) pyrazine is present in the acidic treatmentfluid in a concentration of 0.6 to 1% by weight per total volume of theacidic treatment fluid.

In some embodiments, the acidic treatment fluid consists of the acid andthe pyrazine corrosion inhibitor in water or the acidic treatment fluidconsists of the acid and the pyrazine corrosion inhibitor in anoil-in-water emulsion.

In some embodiments, the acidic treatment fluid further comprises 0.01to 0.5% an intensifier by weight per total volume of the acidictreatment fluid, and wherein the intensifier is at least one selectedfrom the group consisting of CuI, KI, and NaI.

In some embodiments, the intensifier is NaI.

In some embodiments, the acidic treatment fluid further includes 0.001to 0.5% of a sulfur-containing compound by weight per total volume ofthe acidic treatment fluid, wherein the sulfur-containing compound is atleast one selected from the group consisting of a mercapto amino acid orester or peptide thereof, a mercapto heteroarene, a thioglycol compound,and a thiourea compound.

In some embodiments, the sulfur-containing compound is glutathione.

In some embodiments, the acidic treatment fluid further includes anintensifier and a sulfur-containing compound, and wherein the acidictreatment fluid is otherwise substantially free of a supplementarycorrosion inhibitor, a surfactant, and organic solvent, and an additive.

In some embodiments, the acidic treatment fluid consists of the acid,the pyrazine corrosion inhibitor, an intensifier, and asulfur-containing compound in water or the acidic treatment fluidconsists of the acid, the pyrazine corrosion inhibitor, an intensifier,and a sulfur-containing compound in an oil-in-water emulsion.

In some embodiments, the acidic treatment fluid is an aqueous solution.

In some embodiments, the acidic treatment fluid is an oil-in-wateremulsion.

In some embodiments, the acid is HCl and wherein the acidic treatmentfluid comprises 14 to 16 wt. % HCl, based on a total weight of theacidic treatment fluid.

In some embodiments, the oil and gas well is treated with the acidictreatment fluid at a temperature of 25 to 180° C.

In some embodiments, the oil and gas well is treated with the acidictreatment fluid at a temperature of 55 to 65° C.

In some embodiments, the oil and gas well is treated with the acidictreatment fluid at a temperature of 85 to 95° C.

In some embodiments, the metal is carbon steel.

In some embodiments, the acidic treatment fluid is formed downhole byinjecting the acid into the oil and gas well, followed by injecting thepyrazine corrosion inhibitor into the oil and gas well.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIGS. 1A-1C illustrate the molecular structure of (A) pyrazine C, (B)pyrazine E and (C) pyrazine H;

FIGS. 2A-2C are graphs illustrating the impedance plots for X60 steel in15% HCl without and with 0.2% wt. of different types of pyrazinederivatives at 25° C. in (A) Nyquist (B) Bode modulus and (C) Phaseangle representations;

FIG. 3 illustrates the equivalent circuit utilized to fit the EIS data;

FIG. 4 is a graph illustrating the potentiodynamic polarization plotsfor X60 steel in 15% HCl without and with 0.2% wt. of different types ofpyrazine derivatives at 25° C.;

FIGS. 5A-5D are graphs illustrating the intermodulation frequency plotsfor X60 steel in 15% HCl without and with 0.2% wt. of different types ofpyrazine derivatives at 25° C.;

FIGS. 6A-6B are graphs illustrating the variation of corrosion rate withpyrazine C, pyrazine E, and pyrazine H concentration in 15% HCl at (A)60° C. (B) 90° C.;

FIGS. 7A-7B are graphs illustrating the variation of corrosioninhibition efficiency (IE %) with pyrazine C, pyrazine E, and pyrazine Hconcentration in 15% HCl at (A) 60° C. (B) 90° C.;

FIGS. 8A-8E are SEM micrographs of (A) Polished X60 steel, (B) X60 steelcoupon in blank (C) X60 Steel specimen immersed in 1 wt. % pyrazine C(D) X60 Steel specimen immersed in 1% wt. pyrazine E (E) X60 Steelspecimen immersed in 1% wt. pyrazine H;

FIGS. 9A-9C are EDX spectra of X60 steel specimens after immersion in(A) 1 wt. % Pyrazine C (B) 1% wt. Pyrazine E and (C) 1% wt. Pyrazine Hfor 6 h;

FIGS. 10A-10C are graphs illustrating the FTIR spectra of (A) purepyrazine C and that of the base steel+pyrazine, (B) pure pyrazine E andthat of the base steel+pyrazine E and (C) pure pyrazine H and that ofthe base steel+pyrazine H;

FIGS. 11A-11C are 2D-molecular structures of the major microspecies ofthe investigated three pyrazine molecules in strong acidic pH aqueoussolution using Marvin-Beans software;

FIG. 12 is a proposed mechanism of corrosion inhibition in pyrazine C;

FIG. 13 is a proposed mechanism of corrosion inhibition in pyrazine E;and

FIG. 14 is a proposed mechanism of corrosion inhibition in pyrazine H.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, it is understood that other embodimentsmay be utilized and structural and operational changes may be madewithout departure from the scope of the present embodiments disclosedherein.

Definitions

As used herein, the term “fatty” describes a compound with a long-chain(linear) hydrophobic portion made up of hydrogen and anywhere from 6 to26, 8 to 24, 10 to 22, 12 to 20, 14 to 18 carbon atoms, which may befully saturated or partially unsaturated, and optionally attached to apolar functional group such as a hydroxyl group, an amine group, or acarboxyl group (e.g., carboxylic acid). Fatty alcohols, fatty amines,fatty acids, fatty esters, and fatty amides are examples of materialswhich contain a fatty portion, and are thus considered “fatty” compoundsherein. For example, stearic acid, which has 18 carbons total (a fattyportion with 17 carbon atoms and 1 carbon atom from the —COOH group), isconsidered to be a fatty acid having 18 carbon atoms herein.

As used herein, “alkoxylated” or “alkoxylate” refers to compoundscontaining a (poly)ether group (i.e., (poly)oxyalkylene group) derivedfrom reaction with, oligomerization of, or polymerization of one or morealkylene oxides having 2 to 4 carbon atoms, and specifically includes(poly)oxyethylene (derived from ethylene oxide, EO), (poly)oxypropylene(derived from propylene oxide, PO), and (poly)oxybutylene (derived frombutylene oxide, BO), as well as mixtures thereof.

The phrase “substantially free”, unless otherwise specified, describes aparticular component being present in an amount of less than about 1 wt.%, preferably less than about 0.5 wt. %, more preferably less than about0.1 wt. %, even more preferably less than about 0.05 wt. %, yet evenmore preferably 0 wt. %, relative to a total weight of the compositionbeing discussed.

As used herein, the terms “optional” or “optionally” means that thesubsequently described event(s) can or cannot occur or the subsequentlydescribed component(s) may or may not be present (e.g., 0 wt. %).

The term “alkyl”, as used herein, unless otherwise specified, refers toa straight, branched, or cyclic, aliphatic fragment having 1 to 26carbon atoms, preferably 2 to 24, preferably 3 to 22, preferably 4 to20, preferably 5 to 18, preferably 6 to 16, preferably 7 to 14,preferably 8 to 12, preferably 9 to 10. Non-limiting examples include,but are not limited to, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, t-butyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl,3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, lauryl, myristyl,cetyl, stearyl, and the like, including guerbet-type alkyl groups (e.g.,2-methylpentyl, 2-ethylhexyl, 2-proylheptyl, 2-butyloctyl,2-pentylnonyl, 2-hexyldecyl, 2-heptylundecyl, 2-octyldodecyl,2-nonyltridecyl, 2-decyltetradecyl, and 2-undecylpentadecyl), andunsaturated alkenyl and alkynyl variants such as vinyl, allyl,1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl,2-pentenyl, 3-pentenyl, 4-pentenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl,4-hexenyl, 5-hexenyl, oleyl, linoleyl, and the like. Cycloalkyl is atype of cyclized alkyl group. Exemplary cycloalkyl groups include, butare not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,norbornyl, and adamantyl. The term “lower alkyl” is used herein todescribe alkyl groups having 1 to 5 carbon atoms (e.g., methyl, ethyl,n-propyl, etc.).

As used herein, unless otherwise specified, the term “aryl” refers to anaromatic group containing only carbon in the aromatic ring(s), such asphenyl, biphenyl, naphthyl, anthracenyl, and the like. The term“heteroarene” or “heteroaryl” refers to an arene compound or aryl groupwhere at least one carbon atom is replaced with a heteroatom (e.g.,nitrogen, oxygen, sulfur) and includes, but is not limited to, pyridine,pyrimidine, quinoline, isoquinoline, pyrazine, pyridazine, indole,pyrrole, oxazole, thiozole, furan, benzofuran, thiophene,benzothiophene, isoxazole, pyrazole, triazole, tetrazole, indazole,purine, carbazole, imidazole, benzothiozole, and benzimidazole.

As used herein, “alkanoyloxy” groups are alkanoyl groups that are boundto oxygen (—O—C(O)-alkyl), for example, acetyloxy, propionyloxy,butyryloxy, isobutyryloxy, pivaloyloxy, valeryloxy, hexanoyloxy,octanoyloxy, lauroyloxy, and stearoyloxy. “Alkoxycarbonyl” substituentsare alkoxy groups bound to C═O (e.g. —C(O)—Oalkyl), for example methylester, ethyl ester, and pivaloyl ester substitution where the carbonylfunctionality is bound to the rest of the compound.

As used herein, “optionally substituted” means that at least onehydrogen atom is replaced with a non-hydrogen group, provided thatnormal valencies are maintained and that the substitution results in astable compound. Such optional substituents may be selected from aryl,alkoxy, aryloxy, arylalkyloxy, alkanoyloxy, carboxy, alkoxycarbonyl,hydroxy, halo (e.g. chlorine, bromine, fluorine or iodine), amino (e.g.alkylamino, arylamino, arylalkylamino, alkanoylamino, either mono- ordisubstituted), oxo, amido (e.g. —CONH₂, —CONHalkyl, —CONHaryl,—CONHarylalkyl or cases where there are two substituents on onenitrogen), and the like.

As used herein the term “corrosion inhibitor” refers to a substance(s)that prevents or reduces the deterioration of a metal surface byoxidation or other chemical reaction. Corrosive substances that cancause corrosion, particularly of metal surfaces of equipment used duringstimulation operations, include water with high salt contents, acidicinorganic compounds such as hydrochloric acid, hydrofluoric acid, carbondioxide (CO₂) and/or hydrogen sulfide (H₂S), organic acids, andmicroorganisms. Preferred corrosion inhibitors of the present inventionreduce, inhibit and/or prevent the destructive effect such substanceshave on various metal surfaces.

As used herein, the phrase “acid stimulation” or “acidizing” refers tothe general process of introducing an acidic fluid downhole to performat least one of the following functions: (1) to react with and todissolve the area surrounding the well which has been damaged; (2) toreact with and to dissolve rock associated with the geological formationto create small conducting channels (e.g., conducting wormholes) throughwhich the hydrocarbon will flow; and (3) to create a large flow channelby injecting acidic fluids through the well at pressures sufficient tofracture the rock, thus allowing the hydrocarbon to migrate rapidly fromthe rock to the well. Thus, “acid stimulation” or “acidizing” may referto either or both matrix acidizing and fracture acidizing treatments.

Methods of Inhibiting Corrosion

Petroleum oil and natural gas wells are typically subjected to numerouschemical treatments during their production life to enhance operationand protect the integrity of the well and all related equipment. Acidicfluids (HCl, HF, etc.) are often used in stimulation operations such asin matrix acidizing and fracture acidizing treatments, where acidicfluids are injected into the well penetrating the rock pores tostimulate the well to improve flow or to remove damage. In matrixacidizing treatments, acidic treatment fluids are either injected intothe well to react with and to dissolve the area surrounding the well toremove damage around the wellbore, or introduced into the subterraneanformation under pressure (but below the fracture pressure) so that theacidic treatment fluids flow into the pore spaces of the formation andreact with acid-soluble materials contained in the formation, resultingin an increase in the size of the pore spaces and an increase in thepermeability of the formation. In fracture-acidizing treatments, theacidic treatment fluids are introduced above the fracture point of theformation to etch flow channels in the fracture face of the formationand to enlarge the pore spaces in the formation. The increase information permeability from these types of acidic treatments mayincrease the recovery of hydrocarbons from the formation. In most cases,acid stimulation procedures are carried out in calcareous formationssuch as dolomites, limestones, dolomitic sandstones, and the like.

A common problem associated with using acidic treatment fluids insubterranean formations is the corrosion of metal surfaces in piping,tubing, heat exchangers, reactors, downhole tools, and the otherequipment which are exposed to such acid treatments. Further, othercorrosive components such as brines, carbon dioxide, hydrogen sulfide,and microorganisms, may be entrained within the acidic stimulationfluids during stimulation, exacerbating the corrosion problem. Moreover,elevated temperatures are commonly encountered in deeper formationswhich increases the rate of corrosion. Corrosion issues are problematicfor any drilling operation, but are even more troublesome in deep-seaoperations where replacement of corroded equipment is difficult andcostly.

Therefore, it is common practice to employ corrosion inhibitors duringacid stimulation treatments of crude oil and natural gas wells. However,many corrosion inhibitors suffer from poor performance at lowconcentrations and particularly poor performance under high temperaturesand under strongly acidic solutions, for example acidic solutionscontaining greater than or equal to 15 wt. % acid, necessitating theneed for large quantities of corrosion inhibitors to be used. The use oflarge quantities of corrosion inhibitors is extremely undesirable whencorrosion inhibitors are deployed in terms of both cost and fromenvironmental concerns.

The present disclosure thus provides a method for inhibiting corrosionduring acid stimulation in an oil and gas field. The methods involvetreating or otherwise introducing an acidic treatment fluid containingan acid and a pyrazine corrosion inhibitor into an oil and gas well.

Acidic Treatment Fluid

The acidic treatment fluid of the present disclosure generally containsan acid and a pyrazine corrosion inhibitor. The acidic treatment fluidmay optionally include an intensifier, a sulfur-containing compound, orboth. The acidic treatment fluid may further optionally include one ormore of a supplemental corrosion inhibitor, a surfactant, an organicsolvent, and an additive.

Acid

The acidic treatment fluid may contain a variety of acids, preferablywater-soluble acids. Suitable acids include, but are not limited to,hydrochloric acid, formic acid, acetic acid, chloroacetic acid,hydrofluoric acid, sulfuric acid, sulfamic acid, as well as mixturesthereof, for example mud acid (mixtures of HCl and HF). In preferredembodiments, the acid is hydrochloric acid (HCl). Typically, the acidictreatment fluid contains 5 to 28 wt. % of the acid, preferably 7 to 24wt. % of the acid, preferably 9 to 22 wt. % of the acid, preferably 10to 20 wt. % of the acid, preferably 12 to 18 wt. % of the acid,preferably 14 to 16 wt. %, preferably 15 wt. % of the acid(s) (e.g.,HCl), based on a total weight of the acidic treatment fluid, althoughmore concentrated (e.g., about 37 wt. %) or dilute versions may also beused in some circumstances. In some embodiments, the acidic treatmentfluid has a pH of less than 3, preferably less than 2, preferably lessthan 1, preferably less than 0, for example from −2 to 0, or from −1 to0.

In some embodiments, when the acidic treatment fluids are employed inthe acid stimulation methods of the present disclosure, formationchemicals and fluids may become entrained therein. Therefore, inaddition to the acid(s) listed above, the acidic treatment fluids mayalso contain other corrosive agents, including, but not limited to,carbon dioxide, corrosive sulfur species (e.g., hydrogen sulfide,mercaptans, etc.), brine, as well as mixtures thereof.

In some embodiments, the acidic treatment fluid is an aqueous solution,i.e., is substantially free of an oil phase (e.g., contains less than 1wt. %, preferably less than 0.5 wt. %, more preferably less than 0.1 wt.%, even more preferably less than 0.05 wt. %, yet even more preferably 0wt. % of an oil phase, based on a total weight of the acidic treatmentfluid). Preferably, the acidic treatment fluid is injected into the oiland gas well as an aqueous solution for acid stimulation operations, andin doing so, only minor amounts of produced oil and gas from thegeological formation is entrained therein.

In some embodiments, the acidic treatment fluid is a multi-phase mixturecontaining an aqueous phase and an oil phase (and in some cases a gasphase), one example being an emulsion. Such multi-phase mixtures mayalso be effective for acid stimulation operations and simultaneouslyinhibiting corrosion of metal. In some embodiments, the acidic treatmentfluid is an emulsion, preferably a stable emulsion. In preferredembodiments, the acidic treatment fluid is an oil-in-water emulsion. Insome embodiments, the acidic treatment fluid contains at least 5 wt. %,preferably at least 10 wt. %, preferably at least 15 wt. %, preferablyat least 20 wt. %, preferably at least 25 wt. %, and up to 45 wt. %,preferably up to 40 wt. %, preferably up to 35 wt. %, preferably up to30 wt. % of an oil phase, based on a total weight of the acidictreatment fluid.

The oil phase may include a natural oil, a synthetic oil, or both.Examples of oils from natural sources include, but are not limited to,kerosene, diesel oils, crude oils, gas oils, fuel oils, paraffin oils,mineral oils, low toxicity mineral oils, other petroleum distillates,and any combination thereof. Examples of synthetic oils include, but arenot limited to, polyolefins, polydiorganosiloxanes, siloxanes,organosiloxanes, as well as mixtures thereof.

Pyrazine Corrosion Inhibitor

The methods disclosed herein utilize pyrazine corrosion inhibitors,preferably pyrazine corrosion inhibitors which are soluble in water. Thechoice of pyrazine as a corrosion inhibitor is based on its planarstructure that can easily adsorb to the metal surface, sp² hybridizedorbitals that can donate electrons to empty d-orbital of the metal, andthe availability of N atom. The pyrazine corrosion inhibitors of thepresent disclosure may be one or more of 2,3-pyrazine dicarboxylic acid(also referred to herein as pyrazine C), pyrazine-2-carboxamide (alsoreferred to herein as pyrazine E), and 2-methoxy-3-(1-methylpropyl)pyrazine (also referred to herein as pyrazine H).

The pyrazine corrosion inhibitor may be used in any amount sufficient toprovide a desired anticorrosive effect. Typically, highly effectiveanticorrosion effects are achieved when the pyrazine corrosion inhibitoris employed in amounts 0.01 to 5%, preferably 0.03 to 4%, preferably0.05 to 3%, preferably 0.08 to 2%, preferably 0.1 to 1.5%, preferably0.15 to 1.3%, preferably 0.2 to 1.2%, preferably 0.3 to 1.1%, preferably0.4 to 1%, preferably 0.5 to 0.9%, preferably 0.55 to 0.8%, preferably0.6 to 0.7%, by weight per total volume of the acidic treatment fluid.Of course, dosages above or below these values may be used in somecircumstances, when appropriate.

In some embodiments, the pyrazine corrosion inhibitor is 2,3-pyrazinedicarboxylic acid. In some embodiments, the 2,3-pyrazine dicarboxylicacid is present in the acidic treatment fluid in a concentration of 0.2to 1%, preferably 0.4 to 0.9%, preferably 0.6 to 0.8%, preferably 0.7 to0.75%, by weight per total volume of the acidic treatment fluid.

In some embodiments, the pyrazine corrosion inhibitor ispyrazine-2-carboxamide. In some embodiments, the pyrazine-2-carboxamideis present in the acidic treatment fluid in a concentration of 0.8 to1%, preferably 0.82 to 0.98%, preferably 0.84 to 0.96%, preferably 0.86to 0.94%, preferably 0.88 to 0.92%, by weight per total volume of theacidic treatment fluid.

In some embodiments, the pyrazine corrosion inhibitor is2-methoxy-3-(1-methylpropyl) pyrazine. In some embodiments, the2-methoxy-3-(1-methylpropyl) pyrazine is present in the acidic treatmentfluid in a concentration of 0.6 to 1%, preferably 0.65 to 0.95%,preferably 0.7 to 0.9%, preferably 0.75 to 0.85%, preferably 0.79 to0.81% by weight per total volume of the acidic treatment fluid.

Without being bound by theory, the pyrazine corrosion inhibitor may be amixed-type inhibitor, i.e., may adsorb to the surface of the metal andreduce both the cathodic and anodic reactions that cause corrosion, andmay thus remain effective at such extremely low dosages. In someembodiments, such as with 2,3-pyrazine dicarboxylic acid and/or2-methoxy-3-(1-methylpropyl) pyrazine, the pyrazine corrosion inhibitormay be a mixed-type inhibitor, but may function to inhibit corrosionpredominantly through the reduction of cathodic reactions. In someembodiments, such as with pyrazine-2-carboxamide, the pyrazine corrosioninhibitor may be a mixed-type inhibitor, but may function to inhibitcorrosion predominantly through the reduction of anodic reactions.

Mixtures of pyrazine corrosion inhibitors may be employed in the methodsherein. In some embodiments, a mixture of two of 2,3-pyrazinedicarboxylic acid, pyrazine-2-carboxamide, and2-methoxy-3-(1-methylpropyl) pyrazine may be employed, preferably amixture of 2,3-pyrazine dicarboxylic acid and pyrazine-2-carboxamide ina ratio of 10:1 to 1:10, preferably 8:1 to 1:8, preferably 6:1 to 1:6,preferably 4:1 to 1:4, preferably 3:1 to 1:3, preferably 2:1 to 1:2,preferably 1:1. In some embodiments, a mixture of 2,3-pyrazinedicarboxylic acid, pyrazine-2-carboxamide, and2-methoxy-3-(1-methylpropyl) pyrazine may be employed (a mixture ofpyrazine C, E, and H). For example, the mixture may contain 10 to 70 wt.%, preferably 20 to 60 wt. %, preferably 30 to 50 wt. % of 2,3-pyrazinedicarboxylic acid, 5 to 45 wt. %, preferably 15 to 35 wt. %, preferably20 to 30 wt. % of pyrazine-2-carboxamide, and 5 to 45 wt. %, preferably15 to 35 wt. %, preferably 20 to 30 wt. % of2-methoxy-3-(1-methylpropyl) pyrazine, each based on a total weight ofthe mixture (weight sum of pyrazine C+pyrazine E+pyrazine H).

In some embodiments, the pyrazine corrosion inhibitor is the onlycorrosion inhibitor present in the acidic treatment fluid. In someembodiments, the acidic treatment fluid consists essentially of, orconsists of, the acid and the pyrazine corrosion inhibitor in water (theacidic treatment fluid is an aqueous solution of the acid and thepyrazine corrosion inhibitor). In some embodiments, the acidic treatmentfluid consists essentially of, or consists of, the acid and the pyrazinecorrosion inhibitor in an oil-in-water emulsion (the acidic treatmentfluid is an emulsion of the acid the pyrazine corrosion inhibitor in oiland water).

Intensifier

In some situations, for example, under particularly harsh conditions,the acidic treatment fluid may optionally further include an intensifierto further diminish the rate of corrosion. Intensifiers generally do notby themselves impart anticorrosive effects, but rather, when used incombination with a corrosion inhibitor, promote or enhance theanticorrosive properties of such corrosion inhibitors. Suitableintensifiers may include, but are not limited to,

-   -   monocarboxylic acid compounds having 1 to 12 carbon atoms or an        ester (including protected carboxylic acid derivatives) or salt        thereof, such as formic acid, acetic acid, glycolic acid,        propionic acids/esters/salts (e.g., propionic acid,        2-hydroxypropionic acid, 3-hydroxypropionic acid,        2-methoxypropionic acid, 3-methoxypropionic acid,        2-hydroxypropionic acid methyl ester, 3-hydroxypropionic acid        methyl ester, 2-methoxypropionic acid methyl ester,        3-methoxypropionic acid methyl ester, sodium        2-hydroxypropionate, sodium 3-hydroxypropionate, sodium        2-methoxypropionate, and sodium 3-methoxypropionate), lactic        acid, butanoic acid, isobutyric acid, pentanoic acid,        2,2-bis(hydroxymethyl)butanoic acid,        2,2-bis(hydroxymethyl)propionic acid,        2-amino-2,4,5-trideoxypentonic acid, 2-methylserine,        3-(acryloyloxy)propanoic acid, 3-ethoxy-2-methyl-3-oxopropanoic        acid, 3-ethoxypropanoic acid,        3-hydroxy-2-(hydroxymethyl)-2-methylpropanoic acid,        3-hydroxy-2,2-dimethylpropanoic acid, 3-hydroxy-2-oxopropanoic        acid, 3-hydroxy-3-methylbutanoic acid, 3-hydroxybutanoic acid,        3-hydroxyproline, 3-methoxy-2-methyl-3-oxopropanoic acid,        3-methoxy-3-oxopropanoic acid, 3-methoxyalanine,        3-methoxybutanoic acid, 3-methoxypropanoic acid,        3-methoxyvaline, 4-amino-3-hydroxybutanoic acid,        4-hydroxy-4-methyltetrahydro-2H-pyran-2-one, ethyl        3-ethoxypropanoate, ethyl 3-hydroxybutanoate,        hydroxydihydro-2(3H)-furanone, lithium        3-hydroxy-2-oxopropanoate, methyl 2-(1-hydroxyethyl)acrylate,        methyl 2-amino-3-hydroxybutanoate, methyl        2-amino-3-hydroxypropanoate hydrochloride, methyl 3,        3-dimethoxypropanoate, methyl        3-hydroxy-2-(hydroxymethyl)-2-methylpropanoate, methyl        3-hydroxy-2,2-dimethylpropanoate, methyl 3-hydroxyhexanoate,        methyl 3-methoxypropanoate, N-acetylserine, potassium        3-methoxy-3-oxopropanoate, serine, sodium 3-hydroxybutanoate,        and threonine, for example, those monocarboxylic        acids/esters/salts/protected derivatives described in WO        2007007025 A1—incorporated herein by reference in its entirety;    -   formates such as C₁-C₄ alkyl formates (e.g., methyl formate and        ethyl formate), aryl formates, and arylalkyl formates (e.g.,        benzyl formate);    -   formamides such as formamide, dimethyl formamide,        1,1′-azobisformamide;    -   metal halides such as sodium chloride, sodium bromide, potassium        bromide, sodium iodide, potassium iodide, copper(I) chloride,        copper(I) iodide, copper(II) chloride, copper(II) iodide,        antimony chloride;    -   as well as combinations thereof.

When employed, the intensifier is preferably at least one selected fromthe group consisting of CuI, KI, and NaI, more preferably NaI.

The intensifier may be pre-mixed with the acid, the pyrazine corrosioninhibitor, and any other optional component to form the acidic treatmentfluid above hole, and the pre-made acidic treatment fluid may beintroduced into the oil and gas well. Alternatively, the intensifier maybe added to the oil and gas well as a separate component and the acidictreatment fluid containing the intensifier may be formed downhole uponmixing.

When employed, the intensifier may be present in a concentration of 0.01to 1%, preferably 0.05 to 0.5%, preferably 0.08 to 0.4%, preferably 0.09to 0.3%, preferably 0.1 to 0.25%, preferably 0.15 to 0.2% by weight pertotal volume of the acidic treatment fluid.

In some embodiments, the acidic treatment fluid is substantially free ofan intensifier. In some embodiments, the acidic treatment fluid issubstantially free of a monocarboxylic acid compound having 1 to 12carbon atoms or an ester or salt derivative thereof. In someembodiments, the acidic treatment fluid is substantially free of a metalhalide (e.g., NaI, CuI, KI).

Sulfur-Containing Compound

The acidic treatment fluid may optionally further include a sulfurcontaining compound, which may act to prevent oxidative processes thatcan lead to corrosion, for example. The sulfur containing compound maybe present in the acidic treatment fluid in an amount of 0.001 to 0.5%,preferably 0.002 to 0.4%, preferably 0.004 to 0.3%, preferably 0.006 to0.2%, preferably 0.008 to 0.1%, preferably 0.01 to 0.09%, preferably0.02 to 0.08%, preferably 0.05 to 0.07% by weight per total volume ofthe acidic treatment fluid.

Acceptable sulfur-containing compounds that may be employed in theacidic treatment fluids herein include, but are not limited to,

-   -   a mercapto amino acid or ester or peptide thereof, such as        cysteine, homocysteine, N-acetyl cysteine, a di-, tri-, or        polypeptide of cysteine and at least one other amino acid        (leucine, isoleucine, lysine, threonine, methionine,        phenylalanine, valine, tryptophan, histidine, asparagine,        alanine, arginine, aspartic acid, cysteine, glutamic acid,        glutamine, proline, glycine, tyrosine, and serine), for example,        glutathione (reduced), γ-glutamylcysteine, and the like;    -   a mercapto heteroarene such as any benzoxazole, benzothiazole,        benzoimidizole, thiadiazole, triazole, tetrazole, pyridine,        pyrimidine, quinoline, isoquinoline, pyrazine, pyridazine,        indole, pyrrole, oxazole, thiozole, furan, benzofuran,        thiophene, benzothiophene, isoxazole, pyrazole, indazole,        purine, carbazole, or imidazole which contains mercapto        functionality (—SH), with specific mention being made to        mercaptobenzoxazole, mercaptobenzothiazole,        mercaptobenzoimidazole, 2,5-mercapto-1,3,4-thiadiazole,        1-phenyl-5-mercapto-1H-tetrazole,        5-methyl-1,3,4-thiadiazole-2-thiol,        3-mercapto-4-methyl-4H-1,2,4-triazole,        2-amino-5-mercapto-1,3,4-thiadiazole, 4-mercaptopyridine, and        2-mercaptopyridine;    -   a thioglycol compound such as 2-mercaptoethanol, an S-alkyl        thioglycol, an O-alkyl thioglycol, a thioglycol alkoxylate, or a        thiodiglycol alkoxylated, with specific mention being made to        2-mercaptoethanol, 2-(methylthio)ethanol, 2-(ethylthio)ethanol,        thioglycol ethoxylate, thioglycol propoxylate, thioglycol        butoxylate, thiodiglycol ethoxylate, thiodiglycol propoxylate,        thiodiglycol butoxylate;    -   a thiourea compound, for example, thiourea, N-methylthiourea,        N,N′-dimethylthiourea, tetramethylthiourea, N-ethylthiourea,        N,N′-diethylthiourea, tetraethylthiourea, N-propylthiourea,        N,N′-dipropylthiourea, N-butylthiourea, N,N′-dibutylthiourea,        imidazolidine-2-thione, and tetrahydropyrimidine-2(1H)-thione;        and    -   mixtures thereof.

In preferred embodiments, when employed, the sulfur-containing compoundis glutathione.

In some embodiments, the acidic treatment fluids may be formulated witha mixture of two or more sulfur-containing compounds, for example as amixture of a first and second sulfur-containing compound in a molarratio of 10:1 to 1:10, preferably 8:1 to 1:8, preferably 6:1 to 1:6,preferably 4:1 to 1:4, preferably 2:1 to 1:2, preferably about 1:1.

When employed, a weight ratio of the pyrazine corrosion inhibitor to thesulfur-containing compound may be from 20:1 to 200:1, preferably 40:1 to160:1, preferably 60:1 to 140:1, preferably 80:1 to 120:1, preferably100:1.

In some embodiments, the acidic treatment fluid is substantially free ofa sulfur-containing compound (e.g., glutathione).

In some embodiments, the acidic treatment fluid consists of the acid,the pyrazine corrosion inhibitor, an intensifier, and asulfur-containing compound in water. In some embodiments, the acidictreatment fluid consists of the acid, the pyrazine corrosion inhibitor,an intensifier, and a sulfur-containing compound in an oil-in-wateremulsion.

Supplementary Corrosion Inhibitor

The acidic treatment fluid may also optionally include a supplementarycorrosion inhibitor, which is a term used herein to define anysubstance/compound which imparts or is expected to impart a materialanticorrosive effect when included in the acidic treatment fluid, otherthan the pyrazine corrosion inhibitor and the sulfur-containing compounddescribed above. Therefore, as used herein, the terms pyrazine corrosioninhibitor, sulfur-containing compound, and supplementary corrosioninhibitor are meant to be distinct and separate terms. When used, thesupplementary corrosion inhibitor may be present in amounts of 0.01 to15%, preferably 0.05 to 10%, preferably 0.1 to 8%, preferably 0.5 to 5%,preferably 1 to 2% by weight based on a total volume of the acidictreatment fluid.

Any corrosion inhibitor known to those of ordinary skill in the art maybe used herein as a supplementary corrosion inhibitor. Exemplarysupplementary corrosion inhibitors include, but are not limited to,

-   -   a cinnamaldehyde compound, which are those compounds which        contain an optionally substituted aryl group separated from an        aldehyde moiety (or protecting group thereof) by one unsaturated        carbon-carbon double bond, with said aryl group being        unsubstituted (contain only hydrogen as is the case in        cinnamaldehyde) or substituted with up to 5 substituents        individually selected from the group consisting of an optionally        substituted alkyl, an optionally substituted aryl, an optionally        substituted alkoxy, an optionally substituted alkanoyloxy, a        carboxy, an optionally substituted alkoxycarbonyl, a hydroxy, a        halo, an amino group which may be unsubstituted,        monosubstituted, or disubstituted, a nitro, a cyano, a sulfate        anion, an alkylsulfate, a thiocyano, an optionally substituted        alkylthio, an optionally substituted alkylsulfonyl, an        optionally substituted arylsulfonyl, or an optionally        substituted sulfonamido (e.g., —SO₂NH₂), or wherein two adjacent        substituents together form a methylene dioxy group, with        specific mention being made to cinnamaldehyde,        3,3′-(1,4-phenylene)diacrylaldehyde, p-hydroxycinnamaldehyde,        p-methylcinnamaldehyde, p-ethylcinnamaldehyde,        p-methoxycinnamaldehyde, 2,4,5-trimethoxycinnamaldehyde,        3,4,5-trimethoxycinnamaldehyde, 3,4-dimethoxycinnamaldehyde,        1-ethoxy-2-acetoxycinnamaldehyde,        1-ethoxy-2-hydroxycinnamaldehyde, sinapaldehyde,        2,5-dimethoxy-3,4-methylenedioxycinnamaldehyde,        2-methoxy-4,5-methylenedioxy cinnamaldehyde, coniferyl aldehyde,        2,3-dimethoxy-4,5-methylenedioxycinnamaldehyde,        p-dimethylaminocinnamaldehyde, p-diethylaminocinnamaldehyde,        p-nitrocinnamaldehyde, o-nitrocinnamaldehyde,        3,4-methylenedioxycinnamaldehyde, sodium p-sulfocinnamaldehyde,        p-trimethylammoniumcinnamaldehyde,        p-trimethylammoniumcinnamaldehyde o-methylsulfate,        p-thiocyanocinnamaldehyde, p-chlorocinnamaldehyde,        α-methylcinnamaldehyde, β-methylcinnamaldehyde,        α-chlorocinnamaldehyde, α-bromocinnamaldehyde,        α-butylcinnamaldehyde, α-amylcinnamaldehyde,        α-hexylcinnamaldehyde, α-bromo-p-cyanocinnamaldehyde,        α-ethyl-p-methylcinnamaldehyde, and        p-methyl-α-pentylcinnamaldehyde;    -   an alkoxylated fatty amine, which are compounds having a        long-chain alkyl group made up of hydrogen and anywhere from 6        to 26 carbon atoms, preferably 8 to 22 carbon atoms, preferably        12 to 20 carbon atoms, more preferably 16 to 18 carbon atoms,        bonded to an amine functional group which is alkoxylated, where        the fatty portion may be derived/derivable from fatty acids or        fatty acid mixtures such as caprylic acid, capric acid, lauric        acid, myristic acid, palmitic acid, stearic acid, arachidic        acid, behenic acid, lignoceric acid, cerotic acid, myristoleic        acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid,        vaccenic acid, linoleic acid, linoelaidic acid, α-inolenic acid,        arachidonic acid, eicosapentaenoic acid, erucic acid,        docosahexaenoic acid, tall oil fatty acid (TOFA), coconut oil        fatty acid, tallow fatty acid, and soya fatty acid, and thus may        saturated or may contain sites of unsaturation (e.g., mono-,        di-, tri-, oligo-, or poly-unsaturated), with specific mention        being made to a coconut amine alkoxylate, a stearyl amine        alkoxylate, a palmitoleylamine alkoxylate, a oleylamine        alkoxylate, a tallow amine alkoxylate, a tall oil amine        alkoxylate, a laurylamine alkoxylate, a myristylamine        alkoxylate, a cetylamine alkoxylate, a stearylamine alkoxylate,        a linoleyl amine alkoxylate, a soya amine alkoxylate, as well as        alkoxylated ethylene diamine variants thereof, alkoxylated        trimethylene diamine variants thereof, alkoxylated diethylene        triamine variants thereof, and alkoxylated dipropylene triamine        variants thereof;    -   an imidazoline compound, which are those compounds which can be        generally formed from a reaction between (i) a fatty acid or an        ester derivative thereof, for example a C₁ to C₁₂ alkyl ester        (e.g., methyl, ethyl, etc.) of a fatty acid or a glycerol ester        of a fatty acid, and (ii) a polyamine which contains at least        one ethylene diamine group (in various molar ratios between (i)        and (ii)), such as those imidazoline compounds prepared from        reaction between (i) tall oil fatty acid (TOFA), coconut oil        fatty acid, tallow fatty acid, soya fatty acid, and/or oleic        acid and (ii) any polyamine containing two, three, four, or more        nitrogen groups, which may be primary, secondary, or tertiary        amines, so long as at least one ethylene diamine group is        present that is capable of reacting with a carboxylic acid group        to form an imidazoline structure (e.g., ethylene diamine,        3-hydroxyethyl ethylene diamine, 1,2-diaminopropane,        1,2-diaminocyclohexane, 2,3-diaminobutane,        2,3-diaminobutan-1-ol, propane-1,2,3-triamine,        tris(2-aminoethyl)amine, tetraethylenepentamine (TEPA),        diethylenetriamine (DETA), triethylentetramine (TETA),        aminoethylethanolamine (AEEA), pentaethylene hexamine (PEHA),        and hexaethylene heptamine (HEHA)), with specific mention being        made to 1:1 (molar ratio) TOFA/DETA imidazoline, 2:1 TOFA/DETA        imidazoline, 1:1 TOFA/TETA imidazoline, 2:1 TOFA/TETA        imidazoline, 2:1 TOFA/TETA bis-imidazoline, 1:1 TOFA/TEPA        imidazoline, 2:1 TOFA/TEPA imidazoline, 2:1 TOFA/TEPA        bis-imidazoline, 3:1 TOFA/TEPA bis-imidazoline, 1:1 TOFA/AEEA        imidazoline, 2:1 TOFA/AEEA imidazoline, 1:1 TOFA/polyamine        imidazoline, 2:1 TOFA/polyamine imidazoline, 2:1 TOFA/polyamine        bis-imidazoline, 3:1 TOFA/TEPA polyamine bis-imidazoline, 1:1        Soya/DETA imidazoline, 2:1 Soya/DETA imidazoline, 1:1 Soya/TETA        imidazoline, 2:1 Soya/TETA imidazoline, 2:1 Soya/TETA        bis-imidazoline, 1:1 Soya/TEPA imidazoline, 2:1 Soya/TEPA        imidazoline, 2:1 Soya/TEPA bis-imidazoline, 3:1 TOFA/TEPA        bis-imidazoline, 1:1 Soya/AEEA imidazoline, 2:1 Soya/AEEA        imidazoline, 1:1 Soya/polyamine imidazoline, 2:1 Soya/polyamine        imidazoline, 2:1 Soya/polyamine bis-imidazoline, 1:1 Tallow/DETA        imidazoline, 2:1 Tallow/DETA imidazoline, 1:1 Tallow/TETA        imidazoline, 2:1 Tallow/TETA imidazoline, 2:1 Tallow/TETA        bis-imidazoline, 1:1 Tallow/TEPA imidazoline, 2:1 Tallow/TEPA        imidazoline, 2:1 Tallow/TEPA bis-imidazoline, 3:1 Tallow/TEPA        bis-imidazoline, 1:1 Tallow/AEEA imidazoline, 2:1 Tallow/AEEA        imidazoline, 1:1 Tallow/polyamine imidazoline, 2:1        Tallow/polyamine imidazoline, 2:1 Tallow/polyamine        bis-imidazoline, 3:1 Tallow/TEPA polyamine bis-imidazoline;    -   inorganic metal or organometallic compounds such as chromates,        arsenates, and zinc salts;    -   phosphorous-containing compounds such as (poly)phosphates and        phosphonates;    -   acetylenic alcohols such as propargylic (propargyl) alcohol,        pent-4-yn-1-ol, hexynol, ethyl octynol, octynol,        3-phenyl-2-propyn-1-ol;    -   aldehydes (other than cinnamaldehydes above) such as        crotonaldehyde and aromatic aldehydes such as furfural and        p-anisaldehyde;    -   phenones including alkenyl phenone such as        β-hydroxypropiophenone, phenyl vinyl ketone;    -   nitrogen-containing heterocycles (other than the imidazoline and        the pyrazine corrosion inhibitors described above) such as        piperazine and hexamethylene tetramine;    -   quaternized heteroarenes (e.g., 1-(benzyl)quinolinium chloride);    -   condensation products of carbonyls and amines (e.g., Schiff        bases);    -   polymers, including those obtained from natural sources such as        chitin, collagen, pectin, plant gums such as gum Arabic and guar        gum;    -   as well as mixtures thereof.

In preferred embodiments, the acidic treatment fluid is substantiallyfree of supplementary corrosion inhibitors.

Surfactant

The acidic treatment fluid may optionally include one or moresurfactants. Preferably, surfactants are employed when acidic treatmentfluids are used as oil-in-water emulsions. The surfactant(s), whenpresent, may be included in an amount of 0.001 to 5%, preferably 0.005to 3%, preferably 0.01 to 1%, preferably 0.1 to 0.5%, preferably 0.2 to0.4% by weight based on a total volume of the acidic treatment fluid.Cationic, anionic, non-ionic, and/or amphoteric surfactants may beemployed herein.

Cationic surfactants may include, but are not limited to

-   -   a protonated amine formed from a reaction between a C₆-C₂₆ alkyl        amine compound and an acid (e.g., acetic acid, formic acid,        propionic acid, butyric acid, pentanoic acid, hexanoic acid,        oxalic acid, malonic acid, lactic acid, glyceric acid, glycolic        acid, malic acid, citric acid, benzoic acid, p-toluenesulfonic        acid, trifluoromethanesulfonic acid, hydrochloric acid, nitric        acid, phosphoric acid, sulfuric acid, hydrobromic acid,        perchloric acid, hydroiodic acid, etc.), such as protonated        salts of C₆-C₂₆ alkyl monoamines, C₆-C₂₆ alkyl (poly)alkylene        polyamines, and alkoxylated fatty amines;    -   a protonated C₆-C₂₆ alkyl amidoamine formed from a reaction        between a C₆-C₂₆ alkyl amidoamine compound and an acid (for        example the acids listed above), such as protonated forms of the        amide reaction product between any fatty acid previously listed        (or ester derivative thereof) with a polyamine (e.g.,        putrescine, cadaverine, ethylene diamine,        N¹,N¹-dimethylethane-1,2-diamine,        N¹,N¹-dimethylpropane-1,3-diamine,        N¹,N¹-diethylethane-1,2-diamine,        N¹,N¹-diethylpropane-1,3-diamine, spermidine,        1,1,1-tris(aminomethyl)ethane, tris(2-aminoethyl)amine,        spermine, TEPA, DETA, TETA, AEEA, PEHA, HEHA, dipropylene        triamine, tripropylene tetramine, tetrapropylene pentamine,        pentapropylene hexamine, hexapropylene heptamine, dibutylene        triamine, tributylene tetramine, tetrabutylene pentamine,        pentabutylene hexamine, hexabutylene heptamine), with specific        mention being made to protonated forms of        stearamidopropyldimethylamine, stearamidopropyldiethylamine,        stearamidoethyldiethylamine, stearamidoethyldimethylamine,        palmitamidopropyldimethylamine, palmitamidopropyldiethylamine,        palmitamidoethyldiethylamine, palmitamidoethyldimethylamine,        behenamidopropyldimethylamine, behenamidopropyldiethylmine,        behenamidoethyldiethylamine, behenamidoethyldimethylamine,        arachidamidopropyldimethylamine, arachidamidopropyldiethylamine,        arachidamidoethyldiethylamine, and        arachidamidoethyldimethylamine; and    -   a quaternary ammonium compound made from alkylation with        suitable alkylating agents (e.g., dimethyl sulfate, methyl        chloride or bromide, benzyl chloride or bromide, C₆-C₂₆ alkyl        chloride or bromide, etc.) of a tertiary C₆-C₂₆ alkyl amine, an        alkoxylated (tertiary) amine, or an aprotic nitrogenous        heteroarene (optionally substituted) having at least one        aromatic nitrogen atom with a reactive lone pair of electrons,        with specific mention being made to a C₁₀-C₁₈ alkyl trimethyl        ammonium chloride or methosulfate, a di-C₁₀-C₁₈ alkyl dimethyl        ammonium chloride or methesulfate, a C₁₀-C₁₈ alkyl benzyl        dimethyl ammonium chloride, a methyl quaternized C₆-C₂₂ alkyl        propylene diamine, a methyl quaternized C₆-C₂₂ alkyl propylene        triamine, a methyl quaternized C₆-C₂₂ alkyl propylene        tetraamine, a N—C₁₀-C₁₈ alkyl pyridinium or a quinolinium        bromide or chloride such as N-octyl pyridinium bromide, N-nonyl        pyridinium bromide, N-decyl pyridinium bromide, N-dodecyl        pyridinium bromide, N-tetradecyl pyridinium bromide, N-dodecyl        pyridinium chloride, N-cyclohexyl pyridinium bromide, naphthyl        methyl quinolinium chloride, naphthyl methyl pyridinium        chloride, and cetylpyridinium chloride;    -   as well as mixtures thereof.

Anionic surfactants may include, but are not limited to:

-   -   sulfates, such as alkyl sulfates, alkyl-ester-sulfates, alkyl        ether sulfates, alkyl-alkoxy-ester-sulfate, sulfated        alkanolamides, glyceride sulfates, in particular, sulfates of        fatty alcohols or polyoxyalkylene ethers of fatty alcohols such        as sodium dodecyl sulfate, sodium laureth sulfate, ammonium        lauryl sulfate, potassium lauryl sulfate, sodium myreth sulfate;    -   sulfonates such as dodecyl benzene sulfonate, lower        alkyl-benzene sulfonates, alpha olefin sulfonates,        lignosulfonates, sulfo-carboxylic compounds;    -   phosphates of fatty alcohols or polyoxyalkylene ethers of fatty        alcohols such as cetyl phosphate salts, dicetyl phosphate salts,        ceteth-10-phosphate salts;    -   carboxylate salts of fatty acids, acylamino acids, lactylates,        and/or fatty alcohols/polyoxyalkylene ethers of fatty alcohols        such as sodium stearate, sodium behenoyl lactylate, sodium        isostearoyl lactylate, sodium caproyl lactylate, sodium        laureth-5 carboxylate, sodium laureth-6 carboxylate, sodium        laureth-11 carboxylate;    -   and mixtures thereof.

Non-ionic surfactants may include, but are not limited to:

-   -   alkanolamides of fatty acids, that is, amide reaction products        between a fatty acid and an alkanolamine compound, such as        coconut fatty acid monoethanolamide (e.g., N-methyl coco fatty        ethanol amide), coconut fatty acid diethanolamide, oleic acid        diethanolamide, and vegetable oil fatty acid diethanolamide;    -   alkoxylated alkanolamides of fatty acids, preferably ethoxylated        and/or propoxylated variants of the alkanolamides of fatty acids        using for example anywhere from 2 to 30 EO and/or PO molar        equivalents, preferably 3 to 15 EO and/or PO molar equivalents,        preferably 4 to 10 EO and/or PO molar equivalents, preferably 5        to 8 EO and/or PO molar equivalents per moles of the        alkanolamide of the fatty acid (e.g., coconut fatty acid        monoethanolamide with 4 moles of ethylene oxide);    -   amine oxides, such as N-cocoamidopropyl dimethyl amine oxide and        dimethyl C₆-C₂₂ alkyl amine oxide (e.g., dimethyl coco amine        oxide);    -   fatty esters, such as ethoxylated and/or propoxylated fatty        acids (e.g., castor oil with 2 to 40 moles of ethylene oxide),        alkoxylated glycerides (e.g., PEG-24 glyceryl monostearate),        glycol esters and derivatives, monoglycerides, polyglyceryl        esters, esters of polyalcohols, and sorbitan/sorbitol esters;    -   ethers, such as (i) alkoxylated C₁-C₂₂ alkanols, which may        include alkoxylated C₁-C₅ alkanols, preferably ethoxylated or        propoxylated C₁-C₅ alkanols (e.g., dipropylene glycol n-butyl        ether, tripropylene glycol n-butyl ether, dipropylene glycol        methyl ether, tripropylene glycol methyl ether, diethylene        glycol n-butyl ether, triethylene glycol n-butyl ether,        diethylene glycol methyl ether, triethylene glycol methyl ether)        and alkoxylated C₆-C₂₆ alkanols (including alkoxylated fatty        alcohols), preferably alkoxylated C₇-C₂₂ alkanols, more        preferably alkoxylated C₈-C₁₄ alkanols, preferably ethoxylated        or propoxylated (e.g., cetyl stearyl alcohol with 2 to 40 moles        of ethylene oxide, lauric alcohol with 2 to 40 moles of ethylene        oxide, oleic alcohol with 2 to 40 moles of ethylene oxide,        ethoxylated lanoline derivatives, laureth-3, ceteareth-6,        ceteareth-11, ceteareth-15, ceteareth-16, ceteareth-17,        ceteareth-18, ceteareth-20, ceteareth-23, ceteareth-25,        ceteareth-27, ceteareth-28, ceteareth-30, isoceteth-20,        laureth-9/myreth-9, and PPG-3 caprylyl ether); (ii) alkoxylated        polysiloxanes; (iii) ethylene oxide/propylene oxide copolymers        (e.g., PPG-1-PEG-9-lauryl glycol ether, PPG-12-buteth-16,        PPG-3-buteth-5, PPG-5-buteth-7, PPG-7-buteth-10,        PPG-9-buteth-12, PPG-12-buteth-16, PPG-15-buteth-20,        PPG-20-buteth-30, PPG-28-buteth-35, and PPG-33-buteth-45);        and (iv) alkoxylated alkylphenols;    -   and mixtures thereof.

Amphoteric surfactants may include, but are not limited to:

-   -   C₆-C₂₂ alkyl dialkyl betaines, such as fatty dimethyl betaines        (R—N(CH₃)₂(⁺)—CH₂COO⁻), obtained from a C₆-C₂₂ alkyl dimethyl        amine which is reacted with a monohaloacetate salt (e.g., sodium        monochloroacetate), such as C₁₂-C₁₄ dimethyl betaine        (carboxylate methyl C₁₂-C₁₄ alkyl dimethylammonium);    -   C₆-C₂₂ alkyl amido betaines        (R—CO—NH—CH₂CH₂CH₂—N(CH₃)₂(⁺)—CH₂COO⁻ or        R—CO—NH—CH₂CH₂—N(CH₃)₂(⁺)—CH₂COO⁻), obtained by the reaction of        a monohaloacetate salt (e.g., sodium monochloroacetate) with the        reaction product of either dimethyl amino propylamine or        dimethyl amino ethylamine with a suitable carboxylic acid or        ester derivatives thereof, such as C₁₀-C₁₈ amidopropyl        dimethylamino betaine;    -   C₆-C₂₂ alkyl sultaines or C₆-C₂₂ alkyl amido sultaines, which        are similar to those C₆-C₂₂ alkyl dialkyl betaines or C₆-C₂₂        alkyl amido betaines described above except in which the        carboxylic group has been substituted by a sulfonic group        (R—N(CH₃)₂(⁺)—CH₂CH₂CH₂SO₃ ⁻ or        R—CO—NH—CH₂CH₂CH₂—N(CH₃)₂(⁺)—CH₂CH₂CH₂SO₃ ⁻ or        R—CO—NH—CH₂CH₂—N(CH₃)₂(⁺)—CH₂CH₂CH₂SO₃ ⁻) or a hydroxysulfonic        group (R—N(CH₃)₂(⁺)—CH₂CH(OH)—CH₂SO₃ ⁻ or        R—CO—NH—CH₂CH₂CH₂—N(CH₃)₂(⁺)—CH₂CH(OH)—CH₂SO₃ ⁻ or        R—CO—NH—CH₂CH₂—N(CH₃)₂(⁺)—CH₂CH(OH)—CH₂SO₃ ⁻), such as C₁₀-C₁₈        dimethyl hydroxysultaine and C₁₀-C₁₈ amido propyl dimethylamino        hydroxysultaine;    -   and mixtures thereof.

In some embodiments, the acidic treatment fluid is substantially free ofa surfactant.

Organic Solvent

In preferred embodiments, the base solvent of the acidic treatment fluidis water. However, the acidic treatment fluid may also optionallyinclude one or more organic solvents, which may aid solvation of thevarious ingredients and/or facilitate transfer of the active ingredientsto the appropriate location within the wellbore or geological formation.In preferred embodiments, organic solvent(s) may be added in amounts of1 to 30 vol. %, preferably 3 to 25 vol. %, preferably 5 to 20 vol. %,preferably 8 to 16 vol. %, preferably 10 to 14 vol. %, based on a totalvolume of the acidic treatment fluid. The organic solvent may be atleast one selected from the group consisting of a polar aprotic solvent,an aromatic solvent, a terpineol, a mono alcohol with 1 to 12 carbonatoms, and a polyol with 2 to 18 carbon atoms.

Acceptable organic solvents include, but are not limited to, formamide,dimethyl formamide, dimethyl acetamide, acetone, methyl ethyl ketone,methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol,n-pentanol, n-hexanol, terpineol, menthol, prenol,3-methyl-3-buten-1-ol, 2-ethyl-1-hexanol, 2-ethyl-1-butanol,2-propylheptan-1-ol, 2-butyl-1-octanol, ethylene glycol, diethyleneglycol, triethylene glycol, tetraethylene glycol, ethylene glycol methylether, ethylene glycol ethyl ether, ethylene glycol propyl ether,ethylene glycol butyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, propylene glycol, dipropylene glycol,propylene glycol monomethyl ether, pyrocatechol (1,2-benzenediol),resorcinol (1,3-benzenediol), phenol, cresol, benzyl alcohol,1,3-propanediol, 1,3-butanediol, 2-butoxyethanol, 1,4-butanediol,1,6-hexanediol, glycerol, pentaerythritol, manitol, sorbitol, as well asmixtures thereof. In preferred embodiments, the organic solvent is atleast one selected from the group consisting of acetone, methyl ethylketone, methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol,ethylene glycol, and diethylene glycol.

In preferred embodiments, the acidic treatment fluid is substantiallyfree of an organic solvent.

Additives

The acidic treatment fluids may optionally further include one or moreadditives to modify the properties or functions of the acidic treatmentfluid, as needed. Typically, when present, the additive(s) may beincorporated in an amount of less than 10%, preferably less than 8%,preferably less than 6%, preferably less than 4%, preferably less than2%, preferably less than 1%, preferably less than 0.5%, preferably lessthan 0.1% by weight per total volume of the acidic treatment fluid.

Additive(s) suitable for use in oil and gas well operations are known bythose of ordinary skill in the art, and may include, but are not limitedto,

-   -   viscosity modifying agents e.g., bauxite, bentonite, dolomite,        limestone, calcite, vaterite, aragonite, magnesite, taconite,        gypsum, quartz, marble, hematite, limonite, magnetite, andesite,        garnet, basalt, dacite, nesosilicates or orthosilicates,        sorosilicates, cyclosilicates, inosilicates, phyllosilicates,        tectosilicates, kaolins, montmorillonite, fullers earth,        halloysite, polysaccharide gelling agents (e.g., xanthan gum,        scleroglucan, and diutan) as well as synthetic polymer gelling        agents (e.g., polyacrylamides and co-polymers thereof, see U.S.        Pat. No. 7,621,334—incorporated herein by reference in its        entirety), psyllium husk powder, hydroxyethyl cellulose,        carboxymethylcellulose, and polyanionic cellulose, poly(diallyl        amine), diallyl ketone, diallyl amine, styryl sulfonate, vinyl        lactam, laponite;    -   chelating agents, such as chelating agents useful as        sequesteration agents of metal ions, for example iron control        agents, such as ethylene diamine tetraacetic acid (EDTA),        diethylene triamine pentaacetic acid (DPTA), hydroxyethylene        diamine triacetic acid (HEDTA), ethylene diamine        di-ortho-hydroxy-phenyl acetic acid (EDDHA), ethylene diamine        di-ortho-hydroxy-para-methyl phenyl acetic acid (EDDHMA),        ethylene diamine di-ortho-hydroxy-para-carboxy-phenyl acetic        acid (EDDCHA);    -   stabilizing agents e.g., polypropylene glycol, polyethylene        glycol, carboxymethyl cellulose, hydroxyethyl cellulose,        polysiloxane polyalkyl polyether copolymers, acrylic copolymers,        alkali metal alginates and other water soluble alginates,        carboxyvinyl polymers, polyvinylpyrollidones, polyacrylates;    -   dispersing agents e.g., polymeric or co-polymeric compounds of        polyacrylic acid, polyacrylic acid/maleic acid copolymers,        styrene/maleic anhydride copolymers, polymethacrylic acid and        polyaspartic acid;    -   scale inhibitors e.g., sodium hexametaphosphate, sodium        tripolyphosphate, hydroxyethylidene diphosphonic acid,        aminotris(methylenephosphonic acid (ATMP), vinyl sulfonic acid,        allyl sulfonic acid, polycarboxylic acid polymers such as        polymers containing 3-allyloxy-2-hydroxy-propionic acid        monomers, sulfonated polymers such as vinyl monomers having a        sulfonic acid group, polyacrylates and co-polymers thereof;    -   defoaming agents e.g., silicone oils, silicone oil emulsions,        organic defoamers, emulsions of organic defoamers,        silicone-organic emulsions, silicone-glycol compounds,        silicone/silica adducts, emulsions of silicone/silica adducts;    -   emulsifiers such as a tallow amine, a ditallow amine, or        combinations thereof, for example a 50% concentration of a        mixture of tallow alkyl amine acetates, C16-C18 (CAS 61790-60)        and ditallow alkyl amine acetates (CAS 71011-03-5) in a suitable        solvent such as heavy aromatic naphtha and ethylene glycol;    -   as well as mixtures thereof.

In some embodiments, the acidic treatment fluid is substantially free ofan additive (e.g., viscosity modifying agents, chelating agents,stabilizing agents, dispersing agents, scale inhibitors, and/ordefoaming agents). In some embodiments, the acidic treatment fluid issubstantially free of polymers, including both water-soluble andoil-soluble polymers. In preferred embodiments, the acidic treatmentfluid is substantially free of a polysaccharide (e.g., xanthan gum,scleroglucan, and diutan), a synthetic polymer (e.g., polyacrylamidesand co-polymers thereof), and a quaternary ammonium surfactant.

Oil and Gas Well

The pyrazine corrosion inhibitor of the present disclosure may bedeployed during any upstream (exploration, field development, andproduction operations), midstream (transportation e.g., by pipeline,processing, storage, and distribution), or downstream (manufacturing,refining, wholesale) oil and gas process where metal corrosion is aconcern. However, the pyrazine corrosion inhibitor has been found to beparticularly effective at combating corrosion caused by concentratedacidic fluids, and thus are advantageously employed during upstreamprocesses, more preferably during acid stimulation treatments wherecorrosion caused by highly acidic mediums is a primary concern, evenmore preferably during matrix acidizing treatments.

In some embodiments, the acidic treatment fluid may be an aqueoussolution of the acid and the pyrazine corrosion inhibitor, and anyoptional components.

However, one common problem associated with conventional acidizingtreatment systems is that deeper penetration into the formation is notusually achievable because the acid may be spent before it can deeplypenetrate into the subterranean formation. For instance, conventionalacidizing fluids, such as those that contain sulfuric acid, hydrochloricacid, or a mixture of such acids with hydrofluoric acid, have high acidstrength and quickly react with the formation itself, fines and damagenearest the well bore, and often times do not penetrate the formation toa desirable degree before becoming spent. To achieve improved results,it may often be desirable to maintain the acidic solution in a reactivecondition for as long a period as possible to maximize the degree ofpenetration so that the permeability enhancement produced by the acidicsolution may be increased. The emulsified state of the acid makes itdiffuse at much slower rate, thereby retarding the chemical reactionrate with the formation. Therefore, in some embodiments, the acidictreatment fluid is a multiphase mixture comprising an oil phase and anaqueous phase, for example, an emulsion.

In some embodiments, the acidic treatment fluids may be injected downthe annulus of a well and optionally flushed with solvent. In someembodiments, the acidic treatment fluid is pre-formed above well bycombining the acid (aq.) and the pyrazine corrosion inhibitor, and anyoptional components, followed by injecting the pre-formed acidictreatment fluid downhole for the acid stimulation operation. In someembodiments, the acid (aq.) and the pyrazine corrosion inhibitor (andany optional components) are injected downhole as separate streams,combining downhole to form the acidic treatment fluid for acidstimulation. The pyrazine corrosion inhibitor may be injected before,after, or simultaneously with the acid (aq.) for use in the stimulationprocess.

Likewise, when acidic treatment fluids in the form of multi-phasemixtures are utilized, the methods may involve preforming the acidictreatment fluids containing both the aqueous phase and the oil phaseabove well, then injecting the pre-formed acidic treatment fluid (e.g.,emulsion) downhole for the acid stimulation operation. Alternatively,the methods may involve first injecting the oil phase (e.g., kerosene,diesel oil, crude oil, gas oil, fuel oil, paraffin oil, mineral oil, lowtoxicity mineral oil, other petroleum distillate, polyolefin,polydiorganosiloxane, siloxane, organosiloxane) downhole, followed byinjecting the aqueous phase (acid (aq.), corrosion inhibitor, and anyoptional components) downhole, where the phases are combined downhole toform the multi-phase mixture for acid stimulation.

Injection may proceed through suitable injection lines to areas whereacid stimulation treatment is desired or where corrosion can, or islikely to, occur through capillaries or umbilical lines (in many casesat the wellhead if suitable metallurgy is used downhole). Injection maybe performed manually or it may be automatic, for example, by usingchemical injection pumps. In some embodiments, the acidic treatmentfluid may be stored in a chemical storage tank and a chemical injectionpump associated therewith may be used to introduce the acidic treatmentfluid into the desired location of the operation. In any of the aboveapplications, the acidic treatment fluid or any of its componentscombinable downhole may be injected continuously and/or in batches. Thechemical injection pump(s) can be automatically or manually controlledto inject any amount of the acidic treatment fluid needed for acidizingoperations or any amount of the pyrazine corrosion inhibitor suitablefor inhibiting corrosion.

The acidic treatment fluids may be in contact with many different typesof surfaces on tubing and field equipment that are susceptible tocorrosion. Illustrative examples of which include, but are not limitedto, separation vessels, dehydration units, gas lines, pipelines, coolingwater systems, valves, spools, fittings (e.g., such as those that makeup the well Christmas tree), treating tanks, storage tanks, coils ofheat exchangers, fractionating columns, cracking units, pump parts(e.g., parts of beam pumps), and in particular downhole surfaces thatare most likely to come into contact with the acidic treatment fluidsduring stimulation operations, such as those casings, liners, pipes,bars, pump parts such as sucker rods, electrical submersible pumps,screens, valves, fittings, and the like.

Any metal surface that may come into contact with the acidic treatmentfluid may be protected by the pyrazine corrosion inhibitor of thepresent disclosure. Typical metals found in oil and gas fieldenvironments that may be protected include carbon steels (e.g., mildsteels, high-tensile steels, higher-carbon steels), including AmericanPetroleum Institute (API) carbon steels; high alloy steels includingchrome steels, ferritic alloy steels, austenitic stainless steels,precipitation-hardened stainless steels high nickel content steels;galvanized steel, aluminum, aluminum alloys, copper, copper nickelalloys, copper zinc alloys, brass, ferritic alloy steels, and anycombination thereof. Specific examples of typical oil field tubularsteels include X60, J-55, N-80, L-80, P:105, P110, and high alloy chromesteels such as Cr-9, Cr-13, Cr-2205, Cr-2250, and the like. In preferredembodiments, the methods herein inhibit corrosion of API X-60 carbonsteel.

The pyrazine corrosion inhibitor performs surprisingly well to inhibitcorrosion in highly acidic mediums and at temperatures even up to 180°C., for example at temperatures of 25 to 180° C., preferably 35 to 160°C., preferably 45 to 140° C., preferably 55 to 120° C., preferably 65 to110° C., preferably 75 to 100° C., preferably 85 to 90° C. In preferredembodiments, the oil and gas well is treated with the acidic treatmentfluid at a temperature of 50 to 70° C., preferably 55 to 65° C.,preferably 60° C. In other preferred embodiments, the oil and gas wellis treated with the acidic treatment fluid at a temperature of 80 to100° C., preferably 85 to 95° C., preferably 90° C.

Corrosion rate is the speed at which metals undergo deterioration withina particular environment. The rate may depend on environmentalconditions and the condition or type of metal. Factors often used tocalculate or determine corrosion rate include, but are not limited to,weight loss (reduction in weight of the metal during reference time),area (initial surface area of the metal), time (length of exposure time)and density of the metal. Corrosion rate may be measured according tothe American Society for Testing and Materials (ASTM) standard weightloss (immersion) test (e.g., according to ASTM G31-72 and described inthe Examples), and may be computed using mils penetration per year(mpy).

In some embodiments, the method provides a corrosion rate of 50 to 120mpy, preferably 55 to 105 mpy, preferably 60 to 90 mpy, preferably 65 to85 mpy, preferably 70 to 80 mpy, when the oil and gas well is treatedwith the acidic treatment fluid containing 15 wt. % of the acid at 25°C.

In some embodiments, the method provides a corrosion rate of 400 to 840mpy, preferably 405 to 820 mpy, preferably 410 to 800 mpy, preferably450 to 700 mpy, preferably 500 to 600 mpy, when the oil and gas well istreated with the acidic treatment fluid containing 15 wt. % of the acidand 2,3-pyrazine dicarboxylic acid at 60° C. In some embodiments, themethod provides a corrosion rate of 650 to 800 mpy, preferably 680 to780 mpy, preferably 690 to 760 mpy, preferably 700 to 740 mpy,preferably 710 to 720 mpy, when the oil and gas well is treated with theacidic treatment fluid containing 15 wt. % of the acid andpyrazine-2-carboxamide at 60° C. In some embodiments, the methodprovides a corrosion rate of 760 to 3,000 mpy, preferably 800 to 2,700mpy, preferably 900 to 2,500 mpy, preferably 1,000 to 2,100 mpy,preferably 1,100 to 1,800 mpy, when the oil and gas well is treated withthe acidic treatment fluid containing 15 wt. % of the acid and2-methoxy-3-(1-methylpropyl) pyrazine at 60° C.

In some embodiments, the method provides a corrosion rate of 1,500 to3,000 mpy, preferably 1,600 to 2,900 mpy, preferably 1,700 to 2,800 mpy,preferably 2,000 to 2,700 mpy, preferably 2,400 to 2,600 mpy, when theoil and gas well is treated with the acidic treatment fluid containing15 wt. % of the acid and 2,3-pyrazine dicarboxylic acid at 90° C. Insome embodiments, the method provides a corrosion rate of 1,600 to 9,000mpy, preferably 1,700 to 8,000 mpy, preferably 1,800 to 7,000 mpy,preferably 2,000 to 6,000 mpy, preferably 2,500 to 5,000 mpy when theoil and gas well is treated with the acidic treatment fluid containing15 wt. % of the acid and pyrazine-2-carboxamide at 90° C. In someembodiments, the method provides a corrosion rate of 5,000 to 10,000mpy, preferably 5,500 to 9,500 mpy, preferably 6,000 to 9,000 mpy,preferably 6,500 to 8,500 mpy, preferably 7,000 to 8,000 mpy, when theoil and gas well is treated with the acidic treatment fluid containing15 wt. % of the acid and 2-methoxy-3-(1-methylpropyl) pyrazine at 90° C.

Corrosion inhibition efficiencies (IE %) may be measured by comparingthe corrosion rates obtained from acidic treatment fluids with andwithout corrosion inhibitors using weight loss (immersion) studies,electrochemical impedance spectroscopy (EIS), potentiodynamicpolarization (PDP), Linear polarization resistance (LPR) or othersimilar methods. In some embodiments, the method described hereinachieves a corrosion inhibition efficiency of 40 to 65%, preferably 42to 62%, preferably 44 to 60%, preferably 46 to 58%, preferably 48 to56%, preferably 50 to 54% when the oil and gas well is treated with theacidic treatment fluid at 25° C. In some embodiments, the methoddescribed herein achieves a corrosion inhibition efficiency of 70 to90%, preferably 72 to 88%, preferably 74 to 86%, preferably 76 to 84%,preferably 78 to 82%, preferably 80 to 81% when the oil and gas well istreated with the acidic treatment fluid at 60° C. In some embodiments,the method described herein achieves a corrosion inhibition efficiencyof 66 to 90%, preferably 68 to 88%, preferably 70 to 86%, preferably 72to 84%, preferably 74 to 82%, preferably 76 to 80% when the oil and gaswell is treated with the acidic treatment fluid at 90° C.

Of course, the methods herein do not preclude introduction of otherknown chemical treatments into oil and gas field production anddownstream transportation, distribution, and/or refining systems, andthus the acidic treatment fluids may be used in conjunction with otherchemical treatments known to those of ordinary skill in the art,including, but not limited to, hydrate inhibitors, scale inhibitors,asphaltene inhibitors, paraffin inhibitors, H₂S scavengers, O₂scavengers, emulsion breakers, foamers and de-foamers, and waterclarifiers.

The examples below are intended to further illustrate protocols forpreparing and testing the acidic treatment fluids and are not intendedto limit the scope of the claims.

Where a numerical limit or range is stated herein, the endpoints areincluded. Also, all values and subranges within a numerical limit orrange are specifically included as if explicitly written out.

As used herein the words “a” and “an” and the like carry the meaning of“one or more.”

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

All patents and other references mentioned above are incorporated infull herein by this reference, the same as if set forth at length.

EXAMPLES Experimental

Materials

API X60 steel from a typical pipeline was utilized as coupons to carryout this study. Chemical compositions of the specimen utilized areillustrated in Table 1. The coupons were cut to the dimension 3×3 cm.Several emery papers ranging from grit sizes of 120, 240, 320, 400, 600to 800 were employed in grinding the coupons. The coupons werethoroughly rinsed in distilled water after which they were sonicated inacetone. The coupons were finally dried in air prior to immersion.Analytical grade HCl with percentage purity of 37% (Sigma Aldrich) wasdiluted to 15% HCl acid using distilled water.

TABLE 1 Chemical composition of the X60 steel specimen used for theexperiment. Element Fe Cr C Si Mn Cu Ni Mo Al Nb V Composition <96.20.121 0.125 0.52 l.830 0.296 0.091 0.079 0.043 0.053 0.078 (wt. %)Electrochemical Measurement

The setup employed for the electrochemical techniques consist of counterelectrode (graphite), reference electrode (Ag/AgCl), and workingelectrode (X60 steel). The readings were taken on GamryPotentiostat/Galvanostat/ZRA (Reference 3000) instrument. EIS, LPR, PDP,and EFM, were utilized to investigate corrosion performance of X60 steelin the presence and absence of 2000 ppm concentrations of the threepyrazine derivatives in 15% HCl. EIS readings were taken within 100kHz-0.01 Hz frequency range and ±10 mV amplitude after 3600 s delay forstability to be achieved. PDP measurements were taken between thepotential of ±0.25 V vs. E_(OC) and a scan rate of 0.125 mV/s. LPRreadings were taken at E_(corr)±10 mV and 0.125 mV/s scan rate. EFM wasconducted with a base frequency of 0.01, multiplier A=2, B=5, cycle=4and amplitude=10 mV. Data analysis and curve fittings were performedutilizing Gamry EChem Analyst 5.5 software.

Weight Loss

Weight loss tests were carried out on X60 steel coupons in 15% HCl withvarious concentrations of 2,3-pyrazine dicarboxylic acid (pyrazine C),pyrazine-2-carboxamide (pyrazine E), and 2-methoxy-3-(1-methylpropyl)pyrazine (pyrazine H), for 6 hours at 60 and 90° C. During weight lossmeasurements, each specimen was weighed prior to immersion.

The coupons were immersed in duplicates. After completion, coupons wereretrieved, immersed in 1 M acid solution for 15 s to remove corrosionproducts, thoroughly washed, cleaned, air dried, and reweighed. Thecorrosion rates were calculated in mils per year (mpy) using equation 1:

$\begin{matrix}{{{Corrosion}\mspace{14mu}{rate}\mspace{14mu}({mpy})} = \frac{3.45 \times 10^{6} \times W}{D \times A \times T}} & (1)\end{matrix}$where, W is weight loss (g), A is surface area exposed (cm²), T isexposure time (hrs), and D is density (7.86 g/cm³).

Inhibition efficiency was evaluated from equation 2:

$\begin{matrix}{{\%\mspace{14mu}{IE}} = {\frac{{CR}_{o} - {CR}_{i}}{{CR}_{o}} \times 100}} & (2)\end{matrix}$where CR₀ is corrosion rate of steel in blank and CR, is corrosion ratewith inhibitor.Computational Modeling

Marvin-Beans software was used to model the behavior of the threepyrazine derivatives in strong acidic pH aqueous solutions utilizing asemi-empirical computational technique.

Surface Analysis

FTIR

FTIR analysis of the pure inhibitor and that of the corrosion productwas performed using Shimadzu FTIR-8400S spectrophotometer. Analyses ofthe samples were performed at 400-4000 cm⁻¹ wave number range. FTIRspectra of pure inhibitor and scrapped corrosion products on the steelcoupon after immersion in pyrazine C, E, and H in 15% HCl solutions wereobtained and analyzed.

SEM/EDX Surface morphological features were performed on the couponsafter immersion in 15% acid and with various pyrazine concentrations at6 h at 25° C. using Scanning Electron Microscopy (JOEL JSM-6610LV)operated at accelerating voltage of 20 kV. The associated EDX was usedto provide qualitative information about surface elemental composition.

Results and Discussions

Electrochemical Measurement

Electrochemical Impedance Spectroscopy Studies

FIGS. 2A-2C illustrate Nyquist, Bode and phase impedance plots,respectively, in 15% HCl with 0.2% wt/vol. of three different pyrazinederivatives at 25° C. The Nyquist plot shows semicircular arc over theentire frequency range and was attributed to the occurrence of chargetransfer in the solution. See M. Prabakaran, S. H. Kim, V. Hemapriya, I.M. Chung, Tragia plukenetii extract as an eco-friendly inhibitor formild steel corrosion in HCl M acidic medium, Res. Chem. Intermed. 42(2016) 3703-3719—incorporated herein by reference in its entirety. Theimperfect semicircular nature could be caused by the presence of surfaceinhomogeneities. The increase in the radius of the capacitive arc withthe addition of the pyrazines is a clear indication of inhibition. Thebigger the radius the more effective the inhibition process. Asillustrated in FIGS. 1A-1C, pyrazine E (FIG. 1B) possesses an extra Natom in the structure in comparison to pyrazine C (FIG. 1A) and pyrazineH (FIG. 1C) leading to increased rate of interaction between the N-atomsand the active sites of the metal resulting in adsorption. This suggestcoordination bond formation of Fe with N atoms. Adsorption on the metalsurface may also be enhanced by N atoms by donating pi electrons to themetal surface. See C. Verma, L. O. Olasunkanmi, E. E. Ebenso, M. A.Quraishi, I. B. Obot, Adsorption Behavior of Glucosamine-Based,Pyrimidine-Fused Heterocycles as Green Corrosion Inhibitors for MildSteel: Experimental and Theoretical Studies, J. Phys. Chem. C. 120(2016) 11598-11611—incorporated herein by reference in its entirety.These interactions of nitrogen atoms with the surface of the steel ledto an increased resistance to charge transfer and hence increasedcapacitive arc as presented in FIG. 2A. Differences in radii ofcapacitive arcs of the Nyquist plot demonstrate that the addition of thepyrazine derivatives impeded corrosion by inhibition. The larger theradius of the arc, the higher the efficiency. Double layer and filmcapacitances observed showed that charge transfer processes controlledthe corrosion mechanism. See Y. Hao, L. A. Sani, T. Ge, Q. Fang, Thesynergistic inhibition behaviour of tannic acid and iodide ions on mildsteel in H₂SO₄ solutions, Corros. Sci. 123 (2017) 158-169; H. Gao, Q.Li, Y. Dai, F. Luo, H. X. Zhang, High efficiency corrosion inhibitor8-hydroxyquinoline and its synergistic effect withsodiumdodecylbenzenesulphonate on AZ91D magnesium alloy, Corros. Sci. 52(2010) 1603-1609; and W. Liu, A. Singh, Y. Lin, E. E. Ebenso, L. Zhou,B. Huang, 8-Hydroxyquinoline as an Effective Corrosion Inhibitor for7075 Aluminium Alloy in 3.5% NaCl Solution Wanying, Corros. Sci. 52(2010) 1603-1609—each incorporated herein by reference in theirentirety. EIS data extracted from Nyquist plot are shown in Table 2. Theequivalent circuit employed in fitting the Nyquist plot is illustratedin FIG. 3. The accuracy of the fit was between 7.1-28.2×10⁻⁴ for allplots. The model utilized includes Rs (resistance of the solutionbetween counter and working electrodes), Rf (film resistance), Rct(charge transfer resistance), CPE_(f) (constant phase element of film)and CPE_(dl) (double layer constant phase element). Inhibitor efficiencywas evaluated from equation 3:

$\begin{matrix}{{{{IE}({EIS})}\mspace{14mu}\%} = {\left( {1 - \frac{R_{P}}{R_{P\; I}}} \right) \times 100}} & (3)\end{matrix}$where Rp [sum of R_(ct) and R_(f)] and R_(PI) represent polarizationresistances without and with pyrazine, respectively.

TABLE 2 Impedance parameters for X60 steel in 15% HCl without and with0.2% wt. of different pyrazine derivatives at 25° C. CPE_(f) CPE_(dl)R_(s) Y_(o) R_(f) Y_(o) R_(ct) R_(p) (Ω (μΩs^(n) (Ω (μΩs^(n) (Ω (ΩSystems cm²) cm⁻²) n cm²) cm⁻²) n cm²) cm²) χ² × 10⁻⁴ IE(%) Blank 0.53196.0 0.89 −36.90 1170.0 0.18 96.9 60.0 7.1 — Pyrazine C 0.51 3.7 1.10.70 300.5 0.78 102.2 102.9 11.5 41.7 Pyrazine E 0.49 118.2 0.91 17.4154.7 0.89 115.5 132.9 28.2 54.9 Pyrazine H 0.48 19.4 1.1 1.05 541.20.97 116.3 117.4 13.3 48.9

CPE was used to accurately fit the curve instead of pure capacitor. SeeA. Y. Adesina, Z. M. Gasem, A. Madhan Kumar, Corrosion ResistanceBehavior of Single-Layer Cathodic Arc PVD Nitride-Base Coatings in 1MHCl and 3.5 pct NaCl Solutions, Metall. Mater. Trans. B. 48 (2017) 1-12;and A. K. Singh, E. E. Ebenso, M. A. Quraishi, Corrosion inhibitionbehavior of cefuzonam at mild steel/HCl acid interface, Res. Chem.Intermed. 39 (2013) 3033-3042—each incorporated herein by reference intheir entirety. The impedance of CPE was evaluated as:Z _(CPE) =Y ₀ ⁻¹(jω)^(−n)  (4)where Y₀ is the magnitude of CPE, j is square root of −1, ω is angularfrequency and n is phase shift. See M. Larif, A. Elmidaoui, A. Zarrouk,H. Zarrok, R. Salghi, B. Hammouti, H. Oudda, F. Bentiss, Aninvestigation of carbon steel corrosion inhibition in hydrochloric acidmedium by an environmentally friendly green inhibitor, Res. Chem.Intermed. 39 (2013) 2663-2677—incorporated herein by reference in itsentirety. Capacitance of the double layer (CPE)_(dl) values wereevaluated from equation 5:

$\begin{matrix}{{CPE}_{dl} = \frac{Y\;\omega^{n - 1}}{\sin\left( {n\left( \frac{\pi}{2} \right)} \right)}} & (5)\end{matrix}$

As presented in Table 2, charge transfer resistance increasedsignificantly when inhibitor was added and was attributed to formationof surface film. The surface film protects by isolating the steelsurface from corroding media thereby impeding further charge and masstransfer.

Potentiodynamic Polarization Measurements

Polarization curves for X60 with and without the three pyrazinederivatives are presented in FIG. 4. Tafel extrapolation was employed toacquire the respective electrochemical parameter. These parameters arepresented in Table 3. Inhibitor efficiency was evaluated from corrosioncurrent densities utilizing equation 6:

$\begin{matrix}{{{{IE}({PDP})}\mspace{14mu}\%} = {\left( {1 - \frac{I_{corr}^{I}}{I_{corr}^{B}}} \right) \times 100}} & (6)\end{matrix}$where I^(B) _(corr) is corrosion current density in blank and I^(I)_(corr) is corrosion current density with an inhibitor present. The datain Table 3, showed that, I_(corr) decreased upon the addition of thethree pyrazine derivatives. Pyrazine E exhibited the least I_(corr) andhence higher efficiency. Addition of pyrazine C and H shifts thecathodic Tafel slopes to more cathodic region while the anodic portionand the E_(corr) remains constant as illustrated in FIG. 4. This is aclear indication that pyrazine C and H are mixed typed inhibitors butpredominantly cathodic. Addition ofpyrazine E on the other hand caused asignificant shift in the Ecorr, cathodic and anodic curves as shown inFIG. 4. The behavior of pyrazine E is a clear indication of mixed typeinhibitor. Thus the pyrazine derivatives studied in this work do notonly interfere with dissolution of the metal but also interfere withhydrogen evolution as well. See A. Gülşen, Corrosion inhibition of mildsteel by Laurus nobilis leaves extract as green inhibitor, Res. Chem.Intermed. 38 (2012) 1311-1321—incorporated herein by reference in itsentirety. The observed decrease in corrosion current densities,I_(corr), with the addition of pyrazine derivatives in Table 3,indicates increased protection of X60 steel surface.

TABLE 3 Potentiodynamic polarization (PDP) and Linear polarizationresistance (LPR) parameters for X60 steel in 15% HCl without and with0.2% wt. of different pyrazine derivatives at 25° C. PDP Method LPRMethod E_(corr) β_(a) β_(c) R_(p) (mV vs I_(corr) (mV/ (mV/ C_(R) IE (ΩC_(R) IE Systems Ag/AgCl) (A/cm²) dec) dec) (mpy) (%) cm²) (mpy) (%)Blank −374 357 82.6 90.5 163.1 — 57.9 205.5 — Pyrazine C −386 181 72.6120.7 82.8 49.3 115.4 103.1 49.8 Pyrazine E −320 136 57.0 207.1 61.961.9 138.6 85.9 58.2 Pyrazine H −383 166 67.2 108.3 76.1 53.5 118.7100.3 51.2Linear Polarization Resistance Measurement

Linear polarization resistance measurement was performed to evaluateefficiency of inhibition by the three pyrazine derivatives in 15% HCl.This technique allows corrosion rate to be measured in real time and thetechnique is nondestructive. A small voltage value of 10 mV was chosento avoid permanently disrupting the corrosion process, such that ensuingmeasurement remains accurate. The linear relationship between E/I andI_(corr) are valid at this small voltage value. See S. G. Millard, D.Law, J. H. Bungey, J. Cairns, Environmental influences on linearpolarisation corrosion rate measurement in reinforced concrete, NDT EInt. 34 (2001) 409-417; and L. O. Olasunkanmi, I. B. Obot, M. M.Kabanda, E. E. Ebenso, Some Quinoxalin-6-yl Derivatives as CorrosionInhibitors for Mild Steel in Hydrochloric Acid: Experimental andTheoretical Studies, J. Phys. Chem. C. 119 (2015) 16004-16019—eachincorporated herein by reference in their entirety. Polarizationresistance (Rp) and efficiency values obtained are illustrated in Table3. Efficiency of inhibition was evaluated utilizing equation 7 (See S.A. Umoren, Polypropylene glycol: A novel corrosion inhibitor for ×60pipeline steel in 15% HCl solution, J. Mol. Liq. 219 (2016)946-958—incorporated herein by reference in its entirety):

$\begin{matrix}{{{{IE}({LPR})}\mspace{14mu}\%} = {\left( {1 - \frac{R_{p}^{B}}{R_{p}^{I}}} \right) \times 100}} & (7)\end{matrix}$where R^(B) _(p) is the polarization resistance with no inhibitorpresent and R^(I) _(p) is polarization resistance with an inhibitorpresent. The values presented in Table 3 indicate an increase in thepolarization resistance with the addition of the inhibitors relative tothe uninhibited acid. This behavior corroborates the fact that theaddition of the three pyrazine derivatives inhibits corrosion of steelin this high acidic environment. Addition of pyrazine E increasedpolarization resistance value to 138.6 Ωcm⁻² in contrast to 57.9 Ωcm⁻²obtained in the uninhibited acid. This indicates a clear inhibition ofthe corroding steel in the aggressive 15% HCl. It is apparent that PDPand LPR values are in perfect agreement. Both show similar trends indecreased corrosion rates and increased inhibition efficiencies with theaddition of pyrazine derivatives.

Electrochemical Frequency Modulation

FIGS. 5A-5D presents intermodulation spectra for X60 steel with andwithout the three pyrazine derivatives in 15% HCl at 25° C. EFM is atype of nondestructive method that gives corrosion current directly.Sine waves with two frequencies that are different are simultaneouslyused in the cell. See S. S. Abdel-Rehim, K. F. Khaled, N. S.Abd-Elshafi, Electrochemical frequency modulation as a new technique formonitoring corrosion inhibition of iron in acid media by new thioureaderivative, Electrochim. Acta. 51 (2006) 3269-3277; R. W. Bosch, W. F.Bogaerts, Instantaneous Corrosion Rate Measurement with Small-AmplitudePotential Intermodulation Techniques, Corros. 52 (1996) 204-211; K. F.Khaled, Application of electrochemical frequency modulation formonitoring corrosion and corrosion inhibition of iron by some indolederivatives in molar hydrochloric acid, Mater. Chem. Phys. 112 (2008)290-300—each incorporated herein by reference in their entirety. Theresponse of the current consists of frequencies that are multiples,differences, and sums of the two-frequency inputs. The two-frequencyinputs were very small and were multiples of a base frequency. Thehigher frequency is usually more than the lowest by a factor of two atleast. Response of the current between peaks is quite small. Table 4illustrates the parameters obtained for the various pyrazines. Corrosioncurrent density decreased when the pyrazines were added indicatinginhibition in the 15% HCl. This observation was further authenticated byapproximately equal values of the experimental CF values with thetheoretical values of 2 and 3. Inhibitor efficiency (IE_((EFM)) %)presented in Table 4 was evaluated utilizing equation 8:

$\begin{matrix}{{\%\mspace{14mu}{IE}_{({EFM})}} = {\left( {1 - \frac{I_{corr}^{I}}{I_{corr}^{B}}} \right) \times 100}} & (8)\end{matrix}$where I^(B) _(corr) and I^(I) _(corr) are corrosion current densitieswithout and with an inhibitor, respectively.

TABLE 4 Electrochemical frequency modulation parameters for X60 steel in15% HCl in the absence and presence of 0.2% wt. of different pyrazinederivatives at 25° C. I_(corr) β_(a) β_(c) IE Systems (μA cm⁻²) (mVdec⁻¹) (mV dec⁻¹) CF-2 CF-3 (%) Blank 513.8 110.3 117.2 2.32 3.05 —Pyrazine C 245.2 95.2 103.0 2.59 3.12 52.3 Pyrazine E 181.2 91.1 172.91.97 3.14 64.7 Pyrazine H 214.1 81.9 92.7 1.79 3.02 58.3Weight Loss

The initial assessment of the three pyrazine derivatives at 0.2% wt.concentration in 15% HCl at 25° C. was conducted using electrochemicaltechniques. Weight loss measurements were subsequently adopted toinvestigate the effect of varying concentration and temperature on theinhibition potential of the pyrazine derivatives. Corrosion rates andinhibitor efficiencies in an acidizing environment (15% HCl) withdifferent inhibitor concentrations of three pyrazine derivatives wasmeasured with weight loss technique. The weight loss results aspresented in Tables 5, 6 and 7, indicate that all the derivatives ofpyrazine studied in this work are good corrosion inhibitors especiallywith increase in temperature. See I. B. Obot, Z. M. Gasem, Theoreticalevaluation of corrosion inhibition performance of some pyrazinederivatives, Corros. Sci. 83 (2014) 359-366—incorporated herein byreference in its entirety. Inhibition efficiency followed the order:pyrazine E>pyrazine C>pyrazine H at both 60° C. and at 90° C.investigated.

Effect of Concentration

The corrosion rates and inhibitor efficiencies are presented in Tables5, 6 and 7 for pyrazine C, E and H, respectively. It is evident that,the corrosion rate significantly decreased upon adding the inhibitors.Considering pyrazine C, the corrosion rate significantly decreased from3310 mpy to 839 mpy when 0.2 wt. % of the inhibitor was added. At 60°C., inhibition efficiency was relatively constant even though theconcentration of pyrazine C was increase. This behavior could beattributed to the attainment of equilibrium in the rate ofadsorption-desorption of pyrazine C molecules on the metal surface. Asthe temperature increased from 60° C. to 90° C., it was observed that,the corrosion rate in the blank solution was as high as 16870 mpy. Thishigh corrosion rate in the blank was however drastically reduced to 2990mpy when 0.2% wt. of pyrazine C was added. The corrosion rate furtherdecreased to 2600 mpy when the inhibitor concentration was increased to1 wt. %. As illustrated in FIGS. 6A-6B and FIGS. 7A-7B, it can be seenthat the efficiency of pyrazine C was unchanged with concentration atboth temperatures. At 60° C., the highest efficiency observed was 75.30%and this significantly increased to 84.15% when the temperature wasincreased to 90° C. This can be attributed to stronger adsorption of thepyrazine C molecules on the metal surface.

Considering pyrazine E, as illustrated in Table 6, the corrosion ratedecreased significantly to 721.55 mpy when 0.2 wt % of pyrazine E wasadded at a temperature of 60° C. Increasing the inhibitor concentrationcauses no further change in the corrosion rate and the efficiencyremains reasonably constant. This behavior was attributed to theattainment of equilibrium in the adsorption-desorption rate of thepyrazine E molecules on the metal surface. It is worth noting that at90° C., the inhibition efficiency decreased to 47% when 0.2% wt. of theinhibitor was added and this subsequently increased with the inhibitorconcentration to an efficiency of 74.78%. This indicates that as thetemperature is increased, the effect of concentration becomessignificant. As presented in FIG. 6B, the corrosion rate steadilydecreased when 0.2% wt. of the inhibitor was added while FIG. 7B showeda steady increase in the inhibition efficiency with concentration at 90°C. This behavior could be attributed to both physisorption andchemisorption processes of corrosion inhibitor adsorption.

Considering pyrazine H, FIG. 6A demonstrates that the corrosion ratedecreased with increasing concentration at 60° C. The corrosion ratefollows the same pattern when the temperature was increased to 90° C.(FIG. 6B). At 60° C., efficiency increased from 19% to 53% when theconcentration was increase to 1 wt. % of pyrazine H. As presented inTable 7, it was observed that at 0.2 wt. % concentration of theinhibitor, efficiency increased from 19% to 44% when the temperature wasincreased to 90° C. This increase in efficiency with both temperatureand concentration may be attributed to movement of thedesorption-adsorption equilibrium towards adsorption and thermallyactivated chemisorption and the formation of stronger coordinate bonds.The increase in the efficiency of pyrazine H with increasingconcentration indicates that the inhibition performance of pyrazine H isconcentration dependent as shown in FIGS. 7A-7B at 60 and 90° C.,respectively. See P. Singh, E. E. Ebenso, L. O. Olasunkanmi, I. B. Obot,M. A. Quraishi, Electrochemical, Theoretical, and Surface MorphologicalStudies of Corrosion Inhibition Effect of Green NaphthyridineDerivatives on Mild Steel in Hydrochloric Acid, J. Phys. Chem. C. 120(2016) 3408-3419—incorporated herein by reference in its entirety.

Effect of Formulation Additives

In order to enhance the inhibition efficiency of the three pyrazinederivatives, two formulations were prepared where by 0.1 wt. % of sodiumiodide (NaI) was added to the 1 wt. % concentration of each inhibitorwhile in the second formulation 0.01 wt. % Glutathione (Glu) was addedto the first formulation. As can be observed in Table 5, adding NaI topyrazine C at 60° C. increased the inhibition efficiency from 75% to87%. The efficiency was further increased to 89% when the temperaturewas increased to 90° C. The efficiency was further increased to 90% at90° C. test temperature upon the addition of Glu. The inhibitionperformance enhancement was due the interaction between the ionsresulting from the addition of NaI and Glu in the solution and theinhibitor. NaI and Glu enhanced the inhibition performance by formingintermediate bridges between the positive end of the inhibitors and thepositively charged metal surface. See S. A. Umoren, M. M. Solomon,Journal of Industrial and Engineering Chemistry Effect of halide ions onthe corrosion inhibition efficiency of different organic species—Areview, J. Ind. Eng. Chem. 21 (2015) 81-100; and E. Ituen, O. Akaranta,A. James, Green anticorrosive oil field chemicals from5-hydroxytryptophan and synergistic additives for X80 steel surfaceprotection in acidic well treatment fluids, J. Mol. Liq. 224 (2016)408-419—each incorporated herein by reference in their entirety.Addition of NaI and Glu to pyrazine E at 60° C. led to no significantchange in the inhibitor efficiency but when the temperature wasincreased to 90° C., the inhibitor efficiency increased to 89% as shownin Table 6. Adding NaI and Glu to pyrazine H did not cause anysignificant improvement in the inhibitor performance as compared topyrazine C and E as presented in Table 7.

TABLE 5 Weight loss results for X60 steel in 15% HCl with and withoutdifferent concentrations of Pyrazine C at 60 and 90° C. for 6 h. 60° C.90° C. Weight Corrosion Weight Corrosion System/ loss rate Inhibitionloss rate Inhibition Concentration (g) (mpy) efficiency (%) (g) (mpy)efficiency (%) Blank (15% 1.3577 3310.76 — 6.9182 16870.0 — HCl) 0.2%0.3442 839.33 74.65 1.2264 2990.59 82.27 0.4% 0.3447 840.55 74.61 1.10382691.62 84.04 0.6% 0.3355 818.12 75.28 1.1609 2830.86 83.22 0.8% 0.3353807.63 75.30 1.2040 2935.96 82.59 1.0% 0.3357 818.61 75.27 1.09652673.82 84.15 1% Pyrazine C + 0.1664 405.77 87.74 0.7090 1728.90 89.750.1% NaI 1% Pyrazine C + 0.1697 413.81 87.50 0.6889 1679.89 90.04 0.1%NaI + 0.01% Glu

TABLE 6 Weight loss results for X60 steel in 15% HCl with and withoutdifferent concentrations of Pyrazine E at 60 and 90° C. for 6 h. 60° C.90° C. Weight Corrosion Weight Corrosion System/ loss rate Inhibitionloss rate Inhibition Concentration (g) (mpy) efficiency (%) (g) (mpy)efficiency (%) Blank (15% 1.3577 3310.76 — 6.9182 16870.0 — HCl) 0.2%0.2959 721.55 78.21 3.6379 8871.05 47.42 0.4% 0.3055 744.96 77.49 2.94317176.77 57.46 0.6% 0.2897 706.44 78.66 2.3469 5722.93 66.08 0.8% 0.3049743.50 77.54 1.8002 4389.80 73.98 1.0% 0.2889 704.48 78.72 1.74494254.95 74.78 1% Pyrazine E + 0.2902 707.65 78.63 0.7139 1740.85 89.680.1% NaI 1% Pyrazine E + 0.2814 686.20 79.27 0.7204 1756.70 89.59 0.1%NaI + 0.01% Glu

TABLE 7 Weight loss results for X60 steel in 15% HCl with and withoutdifferent concentrations of Pyrazine H at 60 and 90° C. for 6 h 60° C.90° C. Weight Corrosion Weight Corrosion System/ loss rate Inhibitionloss rate Inhibition Concentration (g) (mpy) efficiency (%) (g) (mpy)efficiency (%) Blank (15% 1.3577 3310.76 — 6.9182 16870.0 — HCl) 0.2%1.0988 2679.43 19.07 3.9959 9744.03 42.24 0.4% 0.8279 2018.84 39.023.8778 9456.04 43.95 0.6% 0.6889 1679.89 49.26 3.6058 8792.77 47.88 0.8%0.6540 1594.78 51.83 3.5621 8686.21 48.51 1.0% 0.6250 1524.07 53.973.3716 8221.67 51.26 1% Pyrazine H + 0.3156 769.59 76.75 2.3362 5696.8466.23 0.1% NaI 1% Pyrazine H + 0.4673 1139.45 65.58 2.1027 5127.45 69.600.1% NaI + 0.01% GluSurface CharacterizationsSEM/EDX

Representative SEM micrographs of the X60 steel coupons utilized arepresented in FIGS. 8A-8E. FIG. 8A illustrates a mirror polished couponwith a very smooth surface. However, the surface of the steel wasseverely damaged when immersed in 15% HCl as shown in FIG. 8B. FIGS. 8C,8D, and 8E illustrate the surface of the steel coupons after they wereimmersed in 15% HCl solution containing pyrazine C, E and H,respectively. It can be seen from FIGS. 8C and 8D that the surfacecoverage of the films formed by pyrazine C and E, respectively, weremuch more than that of pyrazine H, shown in FIG. 8E. The higher thesurface coverage of the film the better the underlying metal isprotected from the corrosive media. It is worth noting that the filmsformed in pyrazine H shown in FIG. 8E were not protective enough hencethe acid was able to attack the active sites on the metal surfaceleading to high corrosion rate as compared to pyrazine C and E that hasrelatively lower corrosion rates at both test temperatures.

EDX was utilized to extract information regarding the surface elementalcomposition. FIGS. 9A-9C illustrate the EDX spectrum of X60 steelspecimens immersed in 1 wt. % of pyrazine C, E and H, respectively. FIG.9A showed peaks of Fe that were largely suppressed in the presence ofpyrazine C compared to that of coupons immersed in pyrazine E and H inFIGS. 9B and 9C, respectively. This clearly indicates that there wasmore metal complex formation in pyrazine C than that of E and H,respectively.

FTIR

FTIR was utilized to probe the mechanism of interaction and ascertainthe functional groups that took part in the adsorption process on themetal surface. FIG. 10A illustrates FTIR results obtained on the purepyrazine C and that of the films scrapped from the base steel immersedin the 1 wt. % solution of pyrazine C. The peaks in the pure inhibitorat 3263 cm⁻¹ was ascribed to O—H stretching which completely disappearedto a very broad peak in 1 wt. % solution of the inhibitor. The peak at2367 cm⁻¹ was assigned to C—N triple bond stretching and was present inthe base steel+pyrazine C at 2359 cm⁻¹. The peak at 1703 cm⁻¹ in thepure inhibitor was ascribed to —C═O bond stretching which disappearedcompletely in 1 wt. % solution of the inhibitor. The peak at 1448 cm⁻¹was assigned to O—H bending and this was observed at 1440 cm⁻¹ for thebase steel in pyrazine C solution. The peaks at 1360-1185 cm⁻¹ in thepure inhibitor were assigned to C—N stretching and these peakscompletely disappeared in the base steel+pyrazine C. The peaks at 872,791, 657 cm⁻¹ were attributed to C—H stretching and were diminished onthe base steel+pyrazine.

FIG. 10B illustrates the IR spectra of pure pyrazine E and that of thebase steel+pyrazine E. The peak at 3409 and 3146 cm⁻¹ were attributed toO—H stretching in the pure inhibitor and were completely diminished to abroad peak in the base steel+pyrazine E. Peaks at 2920 and 2856 cm⁻¹were attributed to N—H stretching's in both the pure inhibitor and basesteel+pyrazine E. The peak at 2359 cm⁻¹ was ascribed to C—N bondstretching and was clearly shown in the base steel+pyrazine E as well.The peak at 1696 cm⁻¹ in the pure inhibitor was attributed to C═O bondstretching, and this was observed in the base steel+pyrazine E at 1652cm⁻¹. The peak at 1622 cm⁻¹ was attributed to N—H bending and wasdiminished in the base steel+pyrazine E. The peak at 1382 cm⁻¹ wasattributed to strong C—N stretching whiles the peaks at 1171 and 1025cm⁻¹ were attributed to medium C—N stretching and these peaks wereentirely diminished in the base steel+pyrazine E except for weak peakseen at 1185. The peaks at 873, 842 and 675 cm⁻¹ were assigned to strongC—H bending in the pure inhibitor and these were diminished in the basesteel+pyrazine E except for the peak at 675 that was observed in thebase steel+pyrazine E.

FIG. 10C illustrates the IR spectra of pure pyrazine H and that of thebase steel+pyrazine H. The peak at 3052 cm⁻¹ in the pure inhibitor wasattributed to strong C—H stretching's and this was completely diminishedin the base steel+pyrazine H. Peaks at 2972 and 2884 cm⁻¹ wereattributed to medium C—H stretching and these peaks completelydiminished in the base steel+pyrazine H. The peak due to C—N stretchingwas present at 2367 cm⁻¹ in both the pure inhibitor and that of the basesteel+pyrazine H. The peak at 1652 cm⁻¹ was attributed to weak C═Nstretching, and this was clearly shown in the base steel+pyrazine H. Thepeaks at 1171, 1135, and 1018 cm⁻¹ were ascribed to C—O stretching andthese were diminished in the base steel+pyrazine H. Peaks at 852, 675and 602 cm⁻¹ were attributed to C—H bending. The peak at 675 cm⁻¹ wasclearly shown in the base steel+pyrazine H. The presence of —OH, —C═N,C═C and aromatic ring provide active sites for inhibitor interactionwith surface of the metal.

Mechanism of Inhibition

The inhibition mechanism of corrosion can be analyzed based on theinhibitor adsorption onto surface of the steel. Adsorption of organiccompounds usually works by either physical or chemical processes andsometimes both adsorption processes occur simultaneously. Factors suchas inhibitor charge, molecular structure and metal surface determinesthe adsorption process. The three pyrazine derivatives studied containfunctional groups such as aromatic ring, C═O, C—O, OH, N—H, C═C, and Nthat act as centers of adsorption during the inhibitor adsorptionprocess and the ability of these functional groups to transfer anelectron to the d-orbital of the metal is significant in the adsorptionprocess. See D. Q. Dao, T. D. Hieu, T. Le Minh Pham, D. Tuan, P. C. Nam,I. B. Obot, DFT study of the interactions between thiophene-basedcorrosion inhibitors and an Fe4 cluster, J. Mol. Model. 23 (2017)260—incorporated herein by reference in its entirety. 2D-molecularstructures of the major microspecies of the investigated three pyrazinemolecules in strong acidic pH aqueous solution obtained using asemi-empirical computational method in Marvin-Beans software areillustrated in FIGS. 11A-11C. It can be clearly seen from FIGS. 11A-11Cthat, only pyrazine H was protonated in the acid (FIG. 11C). Pyrazine Cand E remained neutral molecules in the acid solution. The proposedmechanism of inhibition was based on these calculations coupled with theresults obtained in the FTIR analysis.

The predominant corrosion inhibition mechanism observed in pyrazine Cand E is chemisorption as illustrated in FIGS. 12 and 13, respectively.Adsorption was as a result of chemical interactions of unshared electronpairs of nitrogen and empty d-orbital of Fe. Acceptor-donor interactionsbetween the pi electrons of the aromatic ring and Fe also results ininhibitor adsorption on the surface. The rate of chemisorption increasedwith temperature.

Adsorption process that was believed to have dominated in the presenceof pyrazine H was the protonation of N atom and subsequent adsorption onthe steel by negatively charged Cl⁻ ions through electrostaticinteraction. See I. B. Obot, N. K. Ankah, A. Sorour, Z. M. Gasem, K.Haruna, 8-Hydroxyquinoline as an alternative green and sustainableacidizing oilfield corrosion inhibitor, Sustain. Mater. Technol. 14(2017) 1-10; H. Lgaz, R. Salghi, K. Subrahmanya Bhat, A. Chaouiki,Shubhalaxmi, S. Jodeh, Correlated experimental and theoretical study oninhibition behavior of novel quinoline derivatives for the corrosion ofmild steel in hydrochloric acid solution, J. Mol. Liq. 244 (2017)154-168—each incorporated herein by reference in their entirety. Theproposed mechanism in pyrazine H is illustrated in FIG. 14. The rate ofphysiosorption decreased with increased in temperature. It is clear fromFIGS. 12-14, that immersing steel coupons in the blank HCl resulted inmetal dissolution whereas addition of pyrazine led to inhibitoradsorption on the steel surface through chemisorption andphysiosorption. As seen in FIGS. 12-14, pyrazine adsorbed flat on thesurface of the steel at all coverages and forms a superstructure. See U.W. Hamm, V. Lazarescut, D. M. Kolb, Adsorption of pyrazine on Au(111)and Ag(111) electrodes an ex situ XPS study, J. Chem. Soc. FaradayTrans. 92 (1996) 3785-3790—incorporated herein by reference in itsentirety. This process reduces hydrogen evolution by competing with thehydrogen ions for electrons on the metal. After H₂ evolution, inhibitorgoes back to its neutral state with free lone electron pairs. See P.Singh, V. Srivastava, M. A. Quraishi, Novel quinoline derivatives asgreen corrosion inhibitors for mild steel in acidic medium:Electrochemical, SEM, AFM, and XPS studies, J. Mol. Liq. 216 (2016)164-173—incorporated herein by reference in its entirety. The process isachieved without altering the hydrogen evolution mechanism. See W.Zhang, R. Ma, H. Liu, Y. Liu, S. Li, L. Niu, Electrochemical and surfaceanalysis studies of 2-(quinolin-2-yl)quinazolin-4(3H)-one as corrosioninhibitor for Q235 steel in hydrochloric acid, J. Mol. Liq. 222 (2016)671-679—incorporated herein by reference in its entirety. The differencein inhibition performance of the three pyrazine derivatives studied wasattributed the attachment of the different substituent groups as shownin FIGS. 1A-1C. The three pyrazine derivatives contain nitrogen atomshaving lone electron pairs that could be adsorbed on the metal. Thebetter performance of pyrazine C and E compared to H could partially beattributed the presence of additional bonds such as O—H, C═O and N—Hbonds with available α-electrons that can donate electrons to emptyd-orbital Fe to form covalent bond. See D. Huang, Y. Tu, G. Song, X.Guo, E. T. Al, Inhibition Effects of Pyrazine and Piperazine on theCorrosion of Mg-10Gd-3Y-0.5Zr Alloy in an Ethylene Glycol Solution, 2013(2013) 36-38; and J. Saranya, P. Sounthari, K. Parameswari, S. Chitra,Acenaphtho[1,2-b]quinoxaline and acenaphtho[1,2-b]pyrazine as corrosioninhibitors for mild steel in acid medium, Meas. J. Int. Meas. Confed. 77(2016) 175-185—each incorporated herein by reference in their entirety.

Corrosion of X60 steel was monitored in laboratory simulated wellacidizing conditions with and without different concentrations ofpyrazine C, E and H in 15% HCl at 60° C. and 90° C. for 6 hours andelectrochemical measurements at 25° C. to investigate their inhibitionperformance. The three pyrazine derivatives investigated functioned aseffective corrosion inhibitors on X60 steel corrosion in 15% HCl.However, inhibition efficiency were concentration and temperaturedependent. The addition of sodium Iodide (NaI) and Glutathione (Glu)enhanced the inhibition performance of pyrazine C and E but has nosignificant effect on pyrazine H at 60 and 90° C. Electrochemicalstudies indicate that the three pyrazine derivatives are mixed typedwith pyrazine C and H predominantly cathodic inhibitors whereas pyrazineE is predominantly anodic.

Inhibition performance followed the order: pyrazine E>pyrazineC>pyrazine H at 60° C., while the inhibition efficiency followed theorder: pyrazine C>pyrazine E>pyrazine H at 90° C.

The presence of —OH, —C═N, C═C and aromatic ring provide active sitesfor inhibitor interaction with surface of the metal according to theresults of the FTIR spectroscopy.

SEM-EDX confirms the inhibition effect of three pyrazine derivatives onsteel in 15% HCl as compared to the uninhibited solution.

The invention claimed is:
 1. A method of inhibiting corrosion of a metalduring acid stimulation of an oil and gas well, the method comprising:treating the oil and gas well with an acidic treatment fluid comprising10 to 28 wt. % of an acid, based on a total weight of the acidictreatment fluid, and 0.01 to 5% of a pyrazine corrosion inhibitor byweight per total volume of the acidic treatment fluid, and allowing thepyrazine corrosion inhibitor to contact a surface of the metal in theoil and gas well, wherein the pyrazine corrosion inhibitor inhibitscorrosion of the metal, wherein the pyrazine corrosion inhibitor is atleast one selected from the group consisting of 2,3-pyrazinedicarboxylic acid, and 2-methoxy-3-(1-methylpropyl) pyrazine, whereinthe acidic treatment fluid further comprises 0.01 to 0.5% of anintensifier by weight per total volume of the acidic treatment fluid,and wherein the intensifier is at least one selected from the groupconsisting of CuI, KI, and NaI, and wherein the acidic treatment fluidfurther comprises 0.001 to 0.5% of a sulfur-containing compound byweight per total volume of the acidic treatment fluid, wherein thesulfur-containing compound is at least one selected from the groupconsisting of a mercapto amino acid or ester or peptide thereof, amercapto heteroarene, a thioglycol compound, and a thiourea compound. 2.The method of claim 1, wherein the pyrazine corrosion inhibitor ispresent in the acidic treatment fluid in a concentration of 0.2 to 1% byweight per total volume of the acidic treatment fluid.
 3. The method ofclaim 1, wherein the pyrazine corrosion inhibitor is 2,3-pyrazinedicarboxylic acid, and wherein the 2,3-pyrazine dicarboxylic acid ispresent in the acidic treatment fluid in a concentration of 0.2 to 1% byweight per total volume of the acidic treatment fluid.
 4. The method ofclaim 1, wherein the pyrazine corrosion inhibitor is2-methoxy-3-(1-methylpropyl) pyrazine, and wherein the2-methoxy-3-(1-methylpropyl) pyrazine is present in the acidic treatmentfluid in a concentration of 0.6 to 1% by weight per total volume of theacidic treatment fluid.
 5. The method of claim 1, wherein the acidictreatment fluid consists of the acid and the pyrazine corrosioninhibitor in water or wherein the acidic treatment fluid consists of theacid and the pyrazine corrosion inhibitor in an oil-in-water emulsion.6. The method of claim 1, wherein the intensifier is NaI.
 7. The methodof claim 1, wherein the sulfur-containing compound is glutathione. 8.The method of claim 1, wherein the acidic treatment fluid issubstantially free of a supplementary corrosion inhibitor, a surfactant,and organic solvent, and an additive.
 9. The method of claim 1, whereinthe acidic treatment fluid is an aqueous solution.
 10. The method ofclaim 1, wherein the acidic treatment fluid is an oil-in-water emulsion.11. The method of claim 1, wherein the acid is HCl and wherein theacidic treatment fluid comprises 14 to 16 wt. % HCl, based on a totalweight of the acidic treatment fluid.
 12. The method of claim 1, whereinthe oil and gas well is treated with the acidic treatment fluid at atemperature of 25 to 180′C.
 13. The method of claim 1, wherein the oiland gas well is treated with the acidic treatment fluid at a temperatureof 55 to 65′C.
 14. The method of claim 1, wherein the oil and gas wellis treated with the acidic treatment fluid at a temperature of 85 to 95°C.
 15. The method of claim 1, wherein the metal is carbon steel.
 16. Themethod of claim 1, wherein the acidic treatment fluid is formed downholeby injecting the acid into the oil and gas well, followed by injectingthe pyrazine corrosion inhibitor into the oil and gas well.
 17. Themethod of claim 1, wherein the surface of the metal is part of a casing,a pipe, a pump, a screen, a valve, or a fitting.